A computer just won't boot anymore. Here's a procedure that turned out to be quite useful for debugging such a case. Below are different scenarios.
1) You see the BIOS, but the OS fails to boot:
You're lucky. There are several hundred reasons for this to occur, but this is beyond the scope of this small howto. Please ask the web.
2) The computer beeps several times, but you don't even see the BIOS:
You're still quite lucky. The beeps indicate which hardware component is feeling unhappy. I've never found an official document for these beeps, but they seem to have a pattern:
- * long flatline beep: CPU
* single beep sequence: RAM
* single beep - followed by 3 short beeps: graphic card
Then try booting again.
3) In case (2) fails, or there's no beep at all:
ouch. A non-beeping mainboard is close to a dead mainboard. However, there are still some things you can try:
Remove all hardware which is not vitally necessary, and replace (or re-attach) them step by step.
The classic, by-the-book, approach would therefore be:
a) remove everything except the CPU - then reboot.
(Yes EVERYTHING. even mouse, keyboard, or any PCI card - no matter how trivial you might think it is - remove it!)
Expect the beeps as mentioned above.
b) If there are still no beeps: Remove the CPU - then reboot.
c) If there are still no beeps: Change the power supply (PSU) and put the CPU back in - then reboot.
d) If there are still no beeps: The mainboard's probably dead. sorry.
If there are beeps now, proceed in reverse order and put everything back in.
Good luck!