How do diagnose issue of computer resetting itself constantly, please help!

I'm having an issue with my computer resetting randomly, sometimes it
happens once a day, sometimes it doesn't happen for a few days at a
time and other times it happens many times per day.

It's a P4 with 2gig of ram & gigabyte mainboard, and I have replaced
every piece of hardware on it and it still happens!!!

I've replaced, ram, video card, cpu, power supply (I now have
500watt), main board but not my usb devices.


It basically just does a hard reset but doesn't go into the usual
blue screen, just reboots as if you hit the reset key.

I'm running barely anything on the os of the pc except for office,
antivirus (MacAfee) and virtual server 2005 r2. On the virtual servers
I run my dev environment etc...

At first I thought it was hardware related as it was just recycling the
power, however now I wonder whether is is software related as I have
noticed that when it boots up after a crash and goes into the "inform
Microsoft about this problem" screen, it mentions that a driver
caused the "stop error" but gives no more information than that.

I cant see any dump logs under the windows directory, where are they
usually kept and how do I examine them?

If anyone could help me out, on how to debug this, I would be eternally
grateful.

Thanks Ryan