Massive Slowdown in all games

Ive been surfing for a while to get this fixed and have tried a lot of different things but in the end i keep having the same issue. ill start playing a game and then after a little while of playing the game will start to have massive slow down and i can barely do anything in the game. an example of this would be left 4 dead 2. the second level of the hotel. right after i leave the safe house it seems to just start kicking in if i pause the game and wait for a little bit ill be able to get a little farther before it starts up again. the weird things is when i had vista 64-bit i never had these problems so i am trying to figure out if someone has had this issue before and is able to help.

Overheating computer?
Latest drivers for Video card and all other hardware?
Possible memory leak?

Do your fps just continue to drop or does it get choppy with the fps still good?

i've got the same problem since i reinstall my asus g50VT notebook from vista to win7. I've updated all my drivers from bios upto vid card and all necessary driver updates. still no hope. while playing any games smoothly, after a while massive slowdown occurs then after a while it goes back to normal. and keeps repeating.

btw my fps are still good and the gpu also still fine..

More for those who find this, your GPU is overheating because it cant be cooled properly anymore (dust build up). Clean your fan and heatsink (it may even have something to do with the thermal paste). If this is not the case THEN assume it might be software (OS)...