maybe a silly question, but what is the temperature in your surrounding??? my computer gets very hot in the summer, since it can not get enough fresh (cool) air.
i'm also running on a 3ghz cpu...

you could also try another cpu, it is possible that the cpu is broken and gets to hot, i've seen it a couple of times now, although intel cpu's are more stabel then AMD's..


otherwise try a better cooler, the boxed fan's are barely enough to cool the cpu if your running heavy programs...