CPU usage goes up to 100 percent

I have recently bought a new pc say about 4months back. Its a amd dualcore 6000+ 3.ghz machine. Its got 2mb ram and a nvidia geforce 8400 512mb graphic card.
But the main problem with this machine is any game i am playing gets stuck in between after playing for some time,the cpu usage goes uptp 100 percent and stays there for say about 2 or 3mins and then comes back to normal. Again after some time the game gets stuck and the cpu usage is 100 percent. it happens for all the games i have played till date say nfs undercover,james bond quantum of solace,burnout paradise,call of duty 4 and so on.I have all my drivers and direct x uptodate but the problem still persists.Its really irritating and am not at all bng able to find out whats the problem.Would really be grateful if anybody could help me out