Game Resolution Problems

Im having problems with my new computer when running games. Almost any game i run crashes my computer (restarts the system) I think ive worked out the problem, That being the game crashes at any resolution above 640x480. Games that only work at 640x480 include Call of Duty 4, Battlefield 1942, Serious Sam 2, Half-Life 2, CS:S.

The strange thing is games including Crysis, Stalker and Guild Wars all work fine at 1600x1050 with high settings etc. Thinking it was a driver issue i used a brand new HDD with a fresh windows xp install, latest drivers and bios updates. That didnt solve the problem...so i tried some different memory sticks from my friends computer. Yet i still get the crashes. Ive got a Gigabyte 800w Powersupply for the system. I'm guessing its not a hardware problem otherwise Crysis etc would crash.

Ive checked the event viewer and it shows no error before it crashes, how ever there is an error labled 'nv' "Unknown error on CMDre 00000001 00000080 00000000 00000005 00000006" A bit of research has led me to believe its an PCI-E voltage issue, but if that was the case how does it only effect certain games.

Sorry for the essay. lol

My System:
Intel E6850
Asus Blitz Formula
EVGA 8800gtx
Gigabyte 800w
Corsiar 2gig 1066 ram
22" lcd monitor.

would really like to stay away from vista, unless, of corse it is the only solution to my problem.

Cheers

oh sorry, yeah running xp 32bit
And no overclocking, everything is as it came in its box. Bios is set to system defults.

it was set to auto. i changed it to 100, however I still get the crashes.

All the temps seem normal

Gpu - 59c idle
Cpu - 37c idle
mb - 45c