Blue Screen

When Ever I load any pc game, e.g. stalker, call of duty 1;within the first 20 seconds of playing the game freezes, then blocks of pixels on the screen start going multi-coloured for about a minute and the it blue screens me and dumps the files. This is ONLY when I play on any pc game
My Laptop can definatly run these game no problem, it only started doing it about a week ago.
I was wandering if you could tell me how to fix it as I don't want to have to wait 2 weeks for it to be repaired.

Thanks.