Recently had an issue with a friends machine, completely dead / unresponsive.  Regular troubleshooting steps yield no real reason why the machine would be in such a state, but it is 4 years old and based on the amount of hair, dust and tobacco smoke found in the machine, it's a wonder it ran this long, "Buddy, buy a new machine, it's not worth fixing". 

I acquire another brick in my basement.

Two or three weeks go by, I find I need a cd drive for a test machine I have, remembering the brick, I scavenge the cd-rom and start the machine up, nothing !  Crap, i've just burned up my own test machine !  Sure enough, now I have two complete bricks, and the test machine was running fine before I put in the cd rom from the other machine.  Never have I seen a cd rom fry a system board, but it has to be the root cause. 

Be careful of used parts, you get what you pay for.  You can bet both these bricks are going to the recycling center asap !

In attempting to fix my test machine I had to troubleshoot the system board and put together this list.  It didn't help me, but was interesting to research:

AMI BIOS

Number of Beeps

None
You're supposed to hear at least one beep. If you truly don't hear anything, your computer's power supply is no good. Either that or your motherboard or PC Speaker is broken.


One
One beep is good! Everything is A-OK, that is if you see things on the screen. If you don't see anything, check your monitor and video card first. Is everything connected? If they seem fine, your motherboard has some bad chips on it. First reset the SIMM's and reboot. If it does the same thing, one of the memory chips on the motherboard are bad, and you most likely need to get another motherboard since these chips are soldered on.


Two
Your computer has memory problems. First check video. If video is working, you'll see an error message. If not, you have a parity error in your first 64K of memory. First check your SIMM's. Reseat them and reboot. If this doesn't do it, the memory chips may be bad. You can try switching the first and second banks memory chips. First banks are the memory banks that your CPU finds its first 64K of base memory in. You'll need to consult your manual to see which bank is first. If all your memory tests good, you probably need to buy another motherboard.


Three
Basically the same thing as 2 beeps. Follow that diagnosis above.


Four
Basically the same thing as 2 beeps. Follow that diagnosis above. It could also be a bad timer 1.


Five
Your motherboard is complaining. Try reseating the memory and rebooting. If that doesn't help, you should consider another motherboard. You could probably get away with just replacing the CPU, but that's not too cost-effective. Its just time to upgrade!


Six
The chip on your motherboard that controls your keyboard isn't working. First try another keyboard. If it doesn't help, reseat the chip that controls the keyboard, if it isn't soldered in. If it still beeps, replace the chip if possible. Replace the motherboard if it is soldered in.


Seven
Your CPU broke overnight. Its no good. Either replace the CPU, or buy another motherboard.


Eight
Your video card isn't working. Make sure it is seated well in the bus. If it still beeps, either the whole card is bad or the memory on it is. Best bet is to install another video card.


Nine
Your BIOS is bad. Replace the BIOS.


Ten
Your problem lies deep inside the CMOS. All chips associated with the CMOS will likely have to be replaced. Your best bet is to get a new motherboard.


Eleven
Your cache memory is bad and your computer disabled it for you. You could reactivate it by pressing -Ctrl- -Alt- -Shift-
-+- , but you probably shouldn't. Instead, replace your cache memory


Phoenix BIOS

1-1-3
Your computer can't read the configuration info stored in the CMOS. Replace the motherboard.


1-1-4
Your BIOS needs to be replaced.


1-2-1
You have a bad timer chip on the motherboard. You need a new motherboard.


1-2-2
The motherboard is bad.


1-2-3
The motherboard is bad.


1-3-1
You'll need to replace the motherboard.


1-3-3
Same as AMI BIOS 2 beeps. Replace the motherboard.


1-3-4
The motherboard is bad.


1-4-1
The motherboard is bad.


1-4-2
Some of your memory is bad.


2-_-_
Any combo of beeps after two means that some of your memory is bad, and unless you
want to get real technical, you should probably have the guys in the lab coats test the memory for you. Take it to the shop.


3-1-_
One of the chips on your motherboard is broken. You'll likely need to get another board.


3-2-4
Same as AMI BIOS 6 beeps. Keyboard controller failure.


3-3-4
Your computer can't find the video card. Is it there? If so, try swapping it with another one and see if it works.


3-4-_
Your video card isn't working. You'll need to replace it.


4-2-1
There's a bad chip on the motherboard. You need to buy another board.


4-2-2
First check the keyboard for problems. If nothing, you have a bad motherboard.


4-2-3
Same as 4-2-2.


4-2-4
One of the cards is bad. Try yanking out the cards one by one to isolate the culprit. Replace the bad one. The last possibility is to buy another motherboard.


4-3-1
Replace the motherboard.


4-3-2
See 4-3-1


4-3-3
See 4-3-1


4-3-4
Time of day clock failure. Try running the setup program that comes with the computer. Check the date and time. If that doesn't work, replace the battery. If that doesn't work, replace the power supply. You may have to replace the motherboard, but that is rare.


4-4-1

Your serial ports are acting up. Reseat, or replace, the I/O card. If the I/O is on the motherboard itself, disable them with a jumper (consult your manual to know which one) and then add an I/O card.


4-4-2
See 4-4-1


4-4-3
You math coprocessor is cussing. Run a test program to double-check it. If it is indeed bad, disable it, or replace it. Disabling is fine, because you probably don't need it anyway.