Windows 7: Computer freeze when playing all games !

Hey there.

Im sorry if the same problem have posted on this forum. But i didnt find anything

Right. I installed Windows 7 pro 64 bit yesterday. Complete fresh installation. Everthing went smooth and i installed all drivers for my components. 64 bit drivers.

After installing some games again. Like Borderlands and the left 4 dead 2 demo i started running into a problem. pretty serious one.

Every now and then my computer freeze for about 10 seconds. Nothing works. Not even the sound. After 10 sec the main screen (Dual monitors, extended desktop) goes black and i get the sound from ventrilo while the screen is still black. After some jumping into the game and my desktop i get back into the game and i can continue to play like nothing ever happened

What is weird is that my second monitor works when my main monitor is black

My secundary monitor is a samsung t240 (lcd) and my main monitor is a samsung syncmaster 997 mb (crt) if that has anything to do with anything.
The crt is connected with a VGA connector and the lcd with a dvi connector.

My system is as follows.
Asus rampage formula x48 motherboard.
Intel core 2 duo E8600 3.33 Ghz
His Radeon HD 4870 X2
4gb OCZ ddr2 1066mhz


The freeze problem ocurs randomly. and i have no ideas to anything that can couse it



Is it the 64 bit ati drivers that couse this ?

*Edit*
Another problem is when i alt+tab out of counter strike 1.6.
Main screen goes black and lcd acts like normal

Not sure if it happens in singleplayer. But i know for sure its happening in Multiplayer