"it runs smoothly for half a hour but then it suddenly slows down"
That's a common sign of heat. Try this. Leave the side cover off and point a fan at the machine. If that fixes it, talk to the machines maker about a more permanent fix.
hello i have winxp sp2 intel dualcore 3.0ghz
3 gb of ram nvidia geforce 9500gt 1gb 450w psu
when i play any game like assassins creed ,most wanted, under cover,cod4 or any other game. it runs smoothly for half a hour but then it suddenly slows down fps drops to 30 to 6 fps for 5 to 10 seconds again it raises to 30fps but now only for 5 to 10 sec this cycle goes on i dont know what to do any suggestion i done format upgrading video driver but nothing happened