Well, first off. I haven't played a game or used 3d modeling software on my computer for the last 4 months, so i haven't really tested my video card during that time. But i got Windows 7 64 a month ago and installed it in addition with 4 more gb of memory. I tried playing Borderland.. it worked fine for five minutes and then it just froze... I had to ctrl-alt-delete to get out of it and shut it down. Before freezing, weird polygons started appearing out of no where. So i tried to do a stress test on my gpu with FurMark, and as soon as i run the stability test at my desktop's resolution, the thing turns for a split second and the whole computer freezes, i can't even ctrl-alt delete it.. had to restart from the button. Tried the game and Furmark several times, and coming to the same results all the time.
I want to know how to make sure it is the video card thats shot and not the motherboard or something else.
Windows 7 x64
6gb ddr2 Ram
3 hard drives (250 gb, 500gb, 1tb)
Saphire ATI Radeon x1950 pro with 256mb of memory (PCI-e)
Gigabyte GA-P35-DS3R motherboard
Corsaire 550W PSU
Switch out the card for another, if it works then it's the card.
To rule out:
CPU - run prime95 for several hours, use 3D Marks' CPU test
RAM - run memtest or a RAM benchmarking suite
HDD - I cannot believe that the HDD will cause this, if you are not sure run a benchmark/stress test
PSU - I don't know of a definitive way other than switching it out but underclock the x1950 to as low as it will go, 30%-50% of the original clocks.
Mobo - If RAM, HDD, & CPU work I don't get how the mobo will be broken.
Overall I'm pretty sure that your card is dying/dead.