Possible graphics card error? How can I test?

Hey guys, my computer has been acting very strangely the last week or so. I think it may be the graphics card.

The problem:

My monitor essentially deactivates(Not standby, but like you pulled the monitor cord out), and then the computer freezes. The GPU fan is also spinning up like crazy.

This has happened while playing Civ4, when loading Warcraft 3, while idling at windows.

The interesting thing is when it crashes in the game, I can hear the sounds fine. It plays for about 5 seconds then the sounds lock up.

This is why I think it may be a graphics card issue.
Voltages are all within normal except the the -12v is at -.5. Temperature for GPU is around 65C

Win XP Sp2
Geforce 7900 GS 256 Ram
AMD Athlon 64 X2 3800+


I don't have any extra parts to swap around to test, do you guys know of any good diagnostic software that may help me figure this thing out?

Thanks a ton.

***Edit, The GPU fan was spinning up not the CPU***