I bought an BFG 8800 GT OC2 a while back and I'm having problems with it recently. Before this I had some problems with my motherboard's memory slot giving problems in memtest, then eventually causing crashes, lockups, BSODs, nv4_disp.dll BSODs, purple screens, etc randomly when I played video games.  
 
I replaced the old gfx card for the 8800 gt hoping it'd resolve it, but it didnt. Long story short I RMA'd the board got a 780i and it clears through memtest no problems.  
 
However I'm still having problems with gaming. When I play games (especially Assassin's Creed) for a long while, sometimes the game will lockup and the screen will get plastered with red bars all over it. Then it'll usually change to the next frame with similar stuff, then I'll get a bsod a few seconds later and I'll have to reset.  
 
I changed the cooling on the GT to a zalman cooler and went from 70 to 55 degrees idle, 65 load. I also placed Mosfet heatsinks on all the proper places as per this guide http://www.nvnews.net/vbulletin/sh [...] p?t=102371 so I dont really think its overheating but I could be wrong. I can take pictures of my setup in relation to I'm really stumped as to what to do. I only get these problems when I game so I think its the video card.  
 
Any thoughts on what I should do to fix this problem?

Is it occuring more and more? If so, you may have waited to long before you cooled it down

shingouki have you tryed removeing the drivers for the video card and reistalling them.driver cleaner.boot backup in safe mode,and do drivercleaner in safe mode,then bootback up in regular mode.could be your video drivers corrupted.hope this helps you

Reinstalling my drivers did work for a little while, then it started happening again. I'll try turning off my computer for a little while and see if that helps.

What PSU do you have?

I have...a 700W OCZ GameX Stream

Whats drivers are you using?

I believe I'm using the Guru3D drivers version 174.74 for GeForce cards.

I used those until I was getting crashes and freezes in game. Colors, still showing characters and landscape, but a lil distorted and all sorts of colors. It wasnt artifacts, but driver error. Try using the 169.21 drivers