Crashes and errors.

[Murge 0]

Today i installed dayz.. For the 5th time. It was running all good..

Then suddenly it starts to have HUGE graphical errors.. Textures gone wrong.. Screen filled with grey cubes.

Same happens with Arma 2 OA and Arma 2 this all usually ends to black screen, And then i have to restart computer.

I dont have any problems with other games.

I have

Windows 7

Intel® Core2 Quad CPU Q6600 @ 2.40GHz 2.40GHz

8 Gb ram

ATI radeon hd 4870 X2

ATI radeon hd 4870 X2

I dont know if here is all important. But i want fix to this :(