First, go to my comment here which is still relevent to you:http://www.tomshardware.com/forum/349317-33-graphic-cards-troubles-darkness#t2612853
This sounds a lot like a RAM issue which could be caused by:
1) bad RAM
2) incorrectly seated RAM
3) incorrect BIOS profile (requiring BIOS update)
*Try MEMTEST, updating the BIOS, drivers etc and if you're still stuck we'll proceed from there.