bsod on new build

I just built this rig about a month ago. For the first few weeks everything was fine. Then one day I come home from work and its stuck at the windows loading screen. Reboot and get bsod. After finally getting windows to load my video card appears to be uninstalled. Pop in the windows xp install disc and reformat and it gives me blue screens again. I have been messing with this for the last week and a half and cannot figure out what the problem is. At first I was having some problems just installing windows so I figured my disc was a little scratched and picked up Vista 64-bit but it still crashes on me. I can install windows (sometimes) and even get all the drivers loaded and play some ut3 for a few hours but as soon as I leave the computer idle overnight or during the day while I'm at work I come home and it has crashed. Weird thing is it never crashes while I am playing games or running any intensive apps. I thought it might be my memory not being set properly so I checked that and bumped up the voltage to 2.2 and still the same problems. I suspect my power supply might be the culprit but would like a second opinion before I go out and buy another one. My specs:


E8400 @ 3.0
Gigabyte GA-P35-DS3L
Crucial Ballistix 2gb DDR2-800
BFG 8800GT
Seagate 500gb SATA HD
Ultra X2 550 Watt power supply
Audigy 2 ZS platinum

sounds like a sleep/hibernate problem to me. I've had multiple computers give me problems with that.

have you cleared the CMOS?

Well I used the computer for a good few hours yesterday watching a movie and playing games. Overnight it crashed and it said "modification of system code or a critical data structure was detected". I will try memtest and resetting cmos. If that doesn't work I'll try taking out the sound card.