PC will soft shut down ramdomly. In and out of Windows.

[tweaks_sav]

My buddy's got a PC that will randomly shut down on him.
He has replaced the power supply and also totally wiped out the HD and fresh installed XP.
The event log is clear of any BSOD and System Errors. The system is set to NOT automatically restart on error/BSOD.
The BIOS has been updated and set to defaults.
The RAM has been memtest'ed and came out Ok.
It's a custom build 1GB RAM, MSI 865PE Neo2-P Mobo, XP Pro SP2, 40GB HD.
When I was looking at it, the problem occured while in the BIOS, in windows, etc. When I was in the BIOS, the PC would randomlly just turn off, wait 3-5 seconds, then turn on. In Windows when it happens, it will give the logging off screen, then turn off, wait a few secs, then turn back on.
Any ideas?
Thanks,
-Toby

 

[Darth_Terra1]

could be a power problem in that the Power supply is having trouble maintaining the power it needs to run everything.

 

[N3051M]

or a temperature problem. Check for dust and see how hot the CPU gets. You may need to reapply thermal stuff or replace the HSF if its running too hot.

 

[Rik]

Get speedfan from the downloads section and use it to check voltages and temperatures if the pc will stay on long enough!!!!!! Also, if you have an old power switch, try plugging that in instead of the one in the case just in case the switch is faulty!!!!!