What is causing my computer to lock up?

Only for exprerienced PC repair people:
My computer locks up and the screen goes blank 5 minutes after booting EVERY time. Here's what it's not:
1) I know it is not RAM. I have singled out every stick and ran extensive memory tests. No change in results.
2) It is not software or hard drive. I have booted to a linux bootable CD (hard drive unplugged) and it still locked up 5 minutes after boot.
3) It is not the video card. I have swapped video cards to find the same result.

All fans are running fine; I do not believe it is a heat issue. I do not have another power supply with me, but would that cause the computer to lock up at the exact same time every time? Processor and Motherboard are fairly new - all POST tests look fine with them. I'm running out of parts to swap. Has anyone seen anything exactly like this? Any help would be greatly appreciated. Thanks in advance!

Answers:
Try the bare minimum setup. NO HDD, FDD, ODD and just integrated graphics if possible. This set up should POST and be able to open BIOS menu. Load fail safe defaults, save and exit. If if does not lock up in BIOS menu after 15 to 30 minutes, the problem is software or hardware (the devices you removed) related. Try reinstalling HDD first. If it locks again after 5 mins., it could be HDD or OS. If Win XP, try repairing with this:
http://www.informationweek.com/shared/pr...

If the bare minimum set up freezes in BIOS menu, BIOS could be messed up or mobo is defective. But before you junk your mobo, try running it unscrewed from the case. The heat buildup on the PCB after 5 mins. might be causing it to flex a bit. Part of the circuit may be contacting the case and sending an error message.
try resetting your CMOS battery. if you dont know where that is or how to do it, you can look at the motherboard manufacturers handbook thing
This article might help it covers your problem:

http://www.gamegiants.net/article_info.p...

The answers post by the user, for information only, RunQA.com does not guarantee the right.


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