Graphics Card/ Display Problem In Game and On Desktop

Hi I am having a problem with my computer, when playing games. The problem is that suddenly when playing games such as World of Warcraft and Elder Scrolls IV Oblivion the frame rate in game will drop dramatically then I will be presented with a black screen. The game will recover but I am then presented with little black and white pixels on the screen. These can turn into huge distortions when left. Moreover the little black and white pixels do not stay in one place, some disappear and other appear. When this happen and I quit the game the background picture on my desktop is always gone and the white and black pixels are still there and will be until I restart the computer.

Below are two pictures showing the problem one in game and one on the desktop:

http://i858.photobucket.com/albums/ab141/dsp1989/photo....

http://i858.photobucket.com/albums/ab141/dsp1989/photo2...

I have checked that the graphics card is not overheating. It is generally around 65 to 70 degrees when playing a game although I can up the fan speed manually to decrease the temperature further.

Computer Specs:
ASUS Rampage Xtreme Motherboard
X48 Chipset
Intel Core 2 Quad Q9450 2.66 Ghz
8GB Geil Ultra Series PC3-1700 2133 Mhz (Currently Underclocked to 1600 Mhz)
Coolmaster Real Power M850 (850W)
2x Seagate 250GB HDD set up in raid 0
1x Seagate 320GB HDD used to back up files
Antec 900 Case
Samsung SM2433BW 24" TFT Monitor 1920x1200 20000:1

I have had many troubles when I first had this computer with blue screens and ended up pretty much replacing all of the components in the computer except for the graphics card and processor. (motherboard, hard drive, memory, PSU,) have all been replaced until I changed the make of memory from OCZ to Geil. For some reason my computer didn't like OCZ memory.

That's all the information I can provide for now, and I am hoping that someone can confirm the problem so that i can replace the part of my computer before I return to Uni for my final year.

Many Thanks
David