Friend having slowdowns in games

[Rhoxed]

This one has me stumped, sounds like video is throttling but i dont know

in COD4 my screen will flash for a split second then my fps goes from 250 to about 30. Then after a while the screen will flash again and the fps goes back up. I've never heard of this and all my drivers are good, I noticed this when I went from 32bit vista to 64bit windows7. My system supports 64bit, of course, but I don't know why it's doing that. I'm on an XPS m2010 laptop