The magazine of the Melbourne PC User Group Simple Diagnostics Tom Coleman

There must be at least a million different ways of having an accident or becoming incapacitated that will lead to anything from a trivial to a fatal outcome. Yet you can do a First Aid course in about three weeks that covers just about everything. Makes you wonder. The truth is that there only half a dozen things to learn. You can apply them to just about everything to keep the patient going until you can get them to hospital. After that you can sit back with a warm fuzzy glow knowing you did your bit.

The same thing applies to computing. You don't have to know everything about everything to keep your computer going or at least stop it from dying altogether. There is no way that I can cover all you need to be a computer First Aider in one session any more than I could run a first aid course in one session. I can talk around the subject and get you pointed in the right direction.

Here we go

Three quarters of the things that go wrong with your computer are things that happened or did not happen at start up. So getting to be familiar with the start up is a serious step in the right direction.
 
This is a fairly lightweight treatment of this subject. If you want more info then you will have to look it up in other tomes.

It is convenient to be able to power up the monitor before you turn on the computer. Ten seconds of monitor warm up time enables you to see what is on the monitor as soon as the computer starts.

If you have just had the box open and been fiddling with the innards then you may have dislodged, ever so slightly any one of a dozen cables or contacts. You could even have plugged something in inappropriately. These can introduce anything from a dead computer to a funny coloured screen. I will try to toss in a few of these effects as an aside. Generally I am discussing a normal start up by a normal, functioning, computer.

The power supply in the computer converts the 240 volts AC in the wall to 5 and 12 volts DC for the computer. The 12 volts runs the motors, the hard disk, floppies, fans and so on. The 5 volts runs the electronics. In some cases other components break the 5 volts down a bit more. This does not concern you. It is enough to see that the lights come on (that's the 5 volts) and you can hear the fans and hard disk start to run (that's the 12 volts). That tells you that the power supply is working.

BIOS

The next thing that happens is that the BIOS fires up. Now there's a good computer voodoo word. BIOS! It's enough to make a novice's circuit breaker drop out. It has got to be complicated. We can make it more complicated. Sometimes it is called the ROM BIOS. Spooky!

The ROM bit stands for Read Only Memory. Before you give up on me. The page you are reading now is a form of read only memory. The words are stored on paper instead of a chip but there they are. All you can do with them is read them. You cannot change them. Do you have a CD player? The CDs are another form of Read Only Memory. You can run the disk and read the words or hear the music but you cannot have the violinist play a different tune. You can only read what has been written on the compact disc (CD-ROM).

The BIOS is the name of a program that is written to a chip. All the computer can do is to run the program. Like playing a CD except there are no moving parts. Like a written page except that the one on a chip sends out signals to the computer that instruct it do set some things up and to check a few things. The BIOS is the Basic Input Output System. It is a hard-wired program that sets up the very low-level basics of how the computer will operate.

You can see it checking the memory. Well! Not quite. It counts the amount of memory but these days it does no integrity checking whatsoever. Your memory could be useless and, providing it is still plugged in, it will get counted. If you leave a book on the keyboard you will get a keyboard error message when it checks the keyboard. It makes a number of checks and delivers an error message if it finds something wrong. That error message may be something written to the screen or in some cases a series of long and/or short beeps. You need the documentation that came with the motherboard or go to the BIOS manufacturers Web site to find what they mean.

CMOS Setup

The next thing that happens is the computer loads up some information contained in another chip. This chip is called the CMOS (pronounced SEEMOS) There is some confusion over the naming of the CMOS. Sometimes it is mistakenly called the BIOS, which it is not. There are even CMOS setups that call themselves the BIOS. They have got it wrong.

The CMOS contains information about the computer and its equipment. The user can modify most of this information. Hence the earlier notice to "Press DEL to enter setup."
 
If you press the DELete key in time (see Figure 1) you will be shown the CMOS menu (see Figure 2) and you can modify its contents, at your peril.

Modifying the CMOS is worth a whole issue of PC Update, let alone a simple article so I am going to pass it up. Enough to say that the CMOS contains details of the hard disk and other items that will cause you a lot of grief if you get them wrong. If you want to know more then go and find out. Curiosity is a great asset.

The computer picks up a lot of information about itself from the CMOS. You usually see nothing while the CMOS loads. What happens next depends on a setting in the CMOS. Most CMOS let you choose the sequence of boot devices. That is, where the computer looks to find its start up files.
 
Here is a warning. Whilst you can save a half a second at startup by having the computer go to boot from drive C: first, you will be creating a rod for your back if you don't have it try to start from drive A: first. There are some hard disk problems that do not let you back out to start off the A: drive so make sure that your computer looks at drive A: before trying to start from C: (see Figure 3).

By not having a disk in the floppy drive A: the computer just checks it and then goes and starts from the hard drive C:. If you have a problem with the hard disk drive or the startup files, you need to be able to start from the floppy drive using your startup disk which you should have created long ago using, in Windows, Start|Settings|Control Panel| Add-Remove Programs|Startup Disk|Create Disk

If you do not have a startup disk then your are doing yourself a great disservice. I will not be very sympathetic when you phone me for help.
 
Regardless of whether you are stating from the floppy disk in drive A: or from drive C: pretty much the same thing happens next. Lets assume that you are starting from the hard drive the same as usual.

The information on the drive is stored in little pieces called sectors. The disk is written with rings of sectors, typically 63 sectors per ring. These rings are properly called tracks. Each sector holds 512 bytes, which is a half of a kilobyte.

The first sector on the first side under the first head is called the BOOT SECTOR and is put there when the disk is formatted. For convenience we can regard the Partition Table as part of the boot sector. The partition table is some information that describes how the physical drive is set up. For example the disk could be divided up into two or three or more logical drives. It may or may not be a bootable drive. This is what the partition table is about.

If you have a damaged or missing boot sector the computer thinks the disk is not formatted and you get an error message. "General Failure Reading Drive C:" or whatever. Viruses, stray magnetic fields, operator input or the forces of evil among other things, can damage boot sectors. If the boot sector is damaged you might be able to boot from a floppy and fix it with the command; FDISK /MBR. This is an undocumented command and is not supported by Microsoft.
 
Once the computer reads the boot sector it gets enough information about the drive to be able to use it.
 
With the boot sector read, the computer jumps to the first data sector. The first few sectors on the disk are given over to two areas that keep track of the files and are used for housekeeping. It is the rest of the drive that is given over to storing data and the first of those data sectors must have the beginning of a file called something like IO.SYS. It might be IBMIO.SYS or something similar. It is pretty obvious. Once this file is loaded, the computer then loads a file called something like DOS.SYS. Again the spelling might vary a little. Both of these files are Read Only, Archive, System and Hidden. The initials are R A S H. Easy enough to remember. Because they are hidden they do not usually show in the lists of files and because they are read only you cannot modify them easily. The idea is for you to keep your grubby little fingers off them.

CONFIG.SYS

These two files are the ones that really start to set up the computer. Once they have loaded the computer looks for a file called config.sys. This file is one that the user can edit and modify. Many programs add things to the config.sys with or without your permission. You may see output from the execution of the lines in the CONFIG.SYS. References to HIMEM.SYS and information about various drivers may be displayed. This information is often hidden behind the Windows logo. If there are errors or inappropriate commands in config.sys the computer may simply complain and keep going, or it may hang or reboot. So far you have done nothing. You turned the computer on and after a few screen changes, the computer hangs or dies. It leaves you with a sense of injustice or paranoia. I will suggest a work around shortly.

If there is no config.sys or it is empty then the computer keeps going and loads a file called COMMAND.COM. This is the command interpreter. This is the file that give the computer its smarts and enables you to communicate with the computer.

COMMAND.COM and the files IO.SYS and DOS.SYS are the files that boot the computer and make it work. They must all be of the same version of DOS or Windows. You cannot mix versions with these three. You will usually get a "Bad or Missing Command Interpreter" error message.
 
If you suspect that COMMAND.COM is corrupt, missing or the wrong version there is a quick fix. Boot your computer using the startup disk discussed earlier. The only caution here is that the boot files on the startup disk must be the same version as you want to restore to your hard disk. Boot off the floppy and when you get your A:\> prompt type in SYS C: and press enter. The computer will think about it for a few seconds and then display "System transferred". Take the floppy disk out of drive A: and restart the computer. That should fix it. If not then you have a different problem.

Once COMMAND.COM finishes loading it tries to run a file called AUTOEXEC.BAT. This is a batch file that has some start up commands. It may not exist which is quite OK. If the last line in the AUTOEXEC.BAT is "Win" then Windows will start up. If it is nothing in particular then you may finish up at the DOS prompt.

Step by Step Confirmation

Lets back track to when the boot sector gets read. Almost immediately the Windows logo appears. You must learn to recognize the screen before the logo appears. It may have Starting Windows 98 or some such message but that might come and go too fast to be read. Learn to recognize that screen. If you press F8 (You will not do any harm tapping it repeatedly) a menu will appear. If the Windows logo appears you were a bit too slow. Start tapping sooner.

Once the menu appears you have a number of options. The most interesting ones for now are "Step by Step Confirmation" and "Command prompt only". This latter choice gives access to DOS and lets you edit files and generally interact directly with the computer. This implies that your have some knowledge of DOS and the fundamentals of the computer. Certainly not for raw beginners.

The "Step by Step Confirmation" choice lets you accept or reject each command as Windows loads. Many of the commands will be obscure or meaningless to beginners but you don't need to know much to use it as a diagnostic tool. You just accept everything that is offered. Read the screen before you accept the next command and keep looking for error messages or failure to execute.
 
Clearly if the computer reboots or hangs then you have spotted the command that is giving trouble. Try again only this time saying "No" and rejecting the troublesome command. You might well start successfully. Now that you know where the problem is, you can tackle it.

You can run all of the foregoing tests and commands even when there is nothing wrong with your computer. None of them will upset anything. It will give you a look at what using the command is like. You will feel more confident when something really does run off the rails.

On The Inside

Of course if you have just opened the case and maybe replaced the CPU fan (A very simple, no skill required, operation.) and now your computer will not start or behaves unusually, the chances are you have disturbed something or replaced something incorrectly.
 
We will look at a few common causes of this kind of problem but before we go any further, there is one Golden Rule. It says "never open the box without turning off the power and unplugging the power cable."

I'll say that again because it's very important. Turn off the switch at the wall and unplug the power cord from the back of your computer.

Now to those common causes. The broad grey ribbon cables inside the case have a coloured edge. That is the No 1 wire, which attaches to the No 1 pin. Have a look on the motherboard or the card that the cable plugs into and you will see that in most cases the No 1 pin is marked usually with a 1 or a 2 or both (See Figure 4). Sometimes the pins have a rectangle drawn around then with the No 1 corner bevelled. Other times they will indicate No 1 with a little triangle pointing at the pin.

If you plug the hard disk cable in back-to-front the computer will not start. You won't even get to the BIOS beep. The No 1 pin on the back of the hard disk drive is almost always the end nearest where the power plugs in. The power plug is the one with the red, two blacks and a yellow wire (see Figure 5).
 
If you plug the floppy cable in back-to-front the light on the floppy drive comes on as soon as you power up and stays on.
 
If you do put one of these cables in back-to-front you will not damage anything but it will not work properly until you correct it.

Partially dislodged connections can look ok, but when you push them in they move enough to fix some problems.
 
Most motherboards have Primary and Secondary IDE connections. It confuses the computer no end if you don't plug the correct cable into the correct connection. The hard drive goes into the primary. If you have two hard drives then the one that is drive C: goes into the primary. Many motherboards and plug-in cards are clearly marked, as is the Primary IDE connection on the card shown in figures 4, 6 and 7. With some you may have to look in the manual.

In some cases it is possible to offset the connector and plug the bottom row of holes into the top row of pins. At a glance it looks to be right but on closer examination you can see that there is a row of pins not engaged (see Figures 6 and 7). Beware of damaging pins. If you do happen to bend one or two as shown in figure 7, very gently and slowly straighten them and they should be OK.

Monitor

A funny coloured monitor may mean that the monitor cable is not sitting square and/or firmly attached to the Video plug on the back of the computer. A black screen displaying nothing may means it's not plugged in at all, or the cause could simply be that the brightness is turned down too low.

If you don't feel up to fiddling with the innards of your computer then do a Melb PC Training course. It will give you a direction in which to go. Most importantly it will remove the voodoo. People who cannot use a screwdriver will have difficulty with the course. It pays to be familiar with computer basics too.

There is still a whole lot of trouble shooting and diagnostics associated with Windows but I have stopped short of that because it would mean introducing too many new concepts. I will discuss them some other time.

Reprinted from the February 2002 issue of PC Update, the magazine of Melbourne PC User Group, Australia

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