Windows 7 Blackscreaning when started a game

Hello guys, since I installed Windows 7 I have constant blacscreaning when I start a game ( for example Crysis, Cod 5 ), problem which I didn't have when I used Vista. I reinstalled again Windows 7 but the problem continues and the worst part is that when I get the black screen the copmuter just freeze and I have to restart.
PS my specs are - video 4870 1 gb ; cpu e4500 overclocked to 3.2' ; 4gb ram ; win 7 64 bit.
Thank you in advance for your help :)

Well I manage to fix it :) The problem was in the antivirus program.

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