Screen freezes with green pixels

[Guest]

screen freezes with green pixels while i am playing any new installed game.

i just brought this pc 2 months ago. my configuration is:
2.66 GHz Core 2 quad
3 gb ram,64-bit os win 7 ultimate
geforce xfx 8600 gt

i recently installed win 7 from winxp pro sp2. i thought by reinstalling the latest os things will get better,but it didnt.

now the funny part:
1)DEAD SPACE is working perfectly while in winxp and now also in win 7
2)at the beginning i had rainbow six las vegas installed and it was working perfectly at beginning,but later i purchased CALL OF DUTY MODERN WARFARE 2 and installed it in my pc.
since then all this FREEZING episode began.and after that rainbow six freezes too.but DEAD SPACE, i am still playing perfectly.

look,i have searched in net,most of them have not occurred similar problem like having running a game perfectly while the every other not.
so please leave some suggestions.

 

[r_manic]

Sounds like there's something wrong with your graphics card. I know you're able to play Dead Space fine, but artifacts such as the one you've described indicate a broken GPU. It's still under warranty, right?