Weird problem with computer

I'm not sure if I can exactly explain this, but it's really starting to make me mad.


When I am playing a computer game on an ATI RADEON 9600XT AGP , the games run fine for about a half an hour. All of a sudden I get like major lag.. It's not the kind of lag where the screen jumps around, it's the kind of lag where when you look around it just moves really slow. That's probably the best that I can describe it. In order to fix it, I have to reboot my computer. It's really frustrating. I know that it's not the cards, because I completely uninstalled the card ( Using the ati driver remover) then putting another video card in ( ATI 9200 ) ( And an N-vidia card)
When i exit out of the game, when i try to go on to a website that has flash, it just removes reallly slow.

Every thing on my computer is up to date, ( Including my motherboard.)