Computer Reboots on its own...

[JJ24]

The Situation:
My computer has started rebooting quite randomly...
Sometimes it runs for 5 minutes and reboots, other times for 2-3 hours...
Sometimes it reboots while I am typing a word document, other times while playing a game, and other still while just sitting there with a screen saver.
It does not freeze up or have any visual artifacts on the screen, it does not give error codes or Blue Screens of death. It just reboots straight to the graphics card Post screen.

What I have Done:
I have run Memtest86 through several cycles of all the tests and received no errors.
I have run MBM and Coolmon to monitor core temps and never seen it go above 48 celcius.
I have scanned with latest versions of Spybot, Adaware, AVG.

What I have not done:
I have not added any hardware in several months.
I have not added any software in several months.

System Specs:
Pentium 4 2.6ghz w/HT Processor
Abit IS7-E Motherboard
2x512mb Geil PC3200 Memory
256mb Nvidia Geforce 6800XT Video Card
400w Rosewill Power Supply
2 Optical Drives(IDE)
2 Western Digital HD's(1 IDE, 1 SATA)
No add on cards.


I have concluded it is either a Power supply going bad or a HD going bad. I am leaning towards PSU because I think a bad HD would cause lock-ups not just solid reboots without warning signs.

I post here for additional opinions on what I should do to narrow down the problem, or maybe for ideas of what the problem could be that I do not think of. I will also except your sympathies for my troubled times
Thanks!!!

 

[Evacide]

I think that's a classic sign of a bad PSU...

 

[JJ24]

So the rebooting issue has taken a strange turn...

I cannot boot into Windows under regular mode, it restarted after the WinXP splash screen shows up... However if I press F8 for advanced options and choose Safe Mode, or Safe Mode with networking it loads into windows.

That really really makes me suspect some vital system file got corrupted. But Ive never heard of a corrupt install cause reboots without giving errors or freezing up first. Anyone got any ideas?

 

[montag451]

Try disabling your ACPI options in your BIOS for a start.

The restarting does sound like a bad psu, but it could be a stuck power/reset button as well.
The corruptness may come from starting/shutting down continuously improperly.

If you get into Safe mode, look in your event viewer for any ideas