Need help with a crash problem

I'm having a very aggravating problem with my machine, and no luck tracking down it's source. I'm hoping someone out there might know what to do.

The problem is that when i start my computer up after a night of it being off, it'll boot into windows and as soon as it reaches the desktop, the display will get massively corrupted and no longer recognize input. Occasionally the screen will just blank to a single color, though this is rare. Restarting the machine will eventually work, though it takes a while. Also, changing the bios speed (up or down doesn't seem to matter) sometimes gets the machine running fully. Starting windows in safe mode seems to work, but is no guarantee that running it normally will boot all the way.

Rarely, a game will cause a similar crash. I've mostly seen this happen in team fortress 2 so far.

I've rma'd my video card, and the problem seemed to go away for all of a day, then returned with a vengeance. I've run prime for ~18 hours with no error, memtest for ~18 hours with no errors. I've tried running the machine using either stick of ram alone, but the problem remained. The computer had been running stably for over a year before the problem cropped up.

I don't really know what else i can do to diagnose the problem - I think the problem has to lie in either the motherboard or processor, mostly due to a process of elimination, but can't localize it any further. Any ideas on how i can proceed?

System specs:
Intel q9450 running at 3.4 ghz (425 fsb at 1.3v)
4gb (2x2gb) OCZ platinum pc28000 ram using 5-5-5-18 timings at 2.1v
Gigabyte ga-p35-ds3r rev2.1
corsair 620w power supply
evga gtx280 video card
a pair of 500gb wd caviar drives, each has its own system partition and the error occurs when running from either.
running windows 7 x64

Wonder if its a chipset (p35) problem, had problems with my ds3r 2.0 w/q9650 pass 400 fsb until i changed to a asus p45 mobo. Anyhow gl.

A bit of an update. Today, after the system failed to start up normally, i went to safe mode and uninstalled my nvidia drivers. After reboot, system started fine. Win7 automatically installed display drivers, and on the next reboot system failed to startup.

Is there a known problem with nvidia drivers and win7 x64? Or is this probably a hardware fault? The latter seems unlikely, since i just replaced the card.