This problem started w/ my sons desktop, it would just shut off after a bit of work or stay on for a long time & to get it to unfreeze is to cold boot it, i put a new HDD in & I still have the same issue, RAM is good power supply fan is moving quite as well as all the rest of the fans it has stayed fairly dust free, i'm at a loss ,I have defaulted all the factory settings changed battery & ungraded to a new OS. I still have the same problem. the power light stays on after it has shut down & when upon starting it goes straight to safe mode option page, I start in last good config. reboots again takes 30 sec. to boot & will work again for a while, the only other thing I haven't tried was a graphic card replace, i'm onboard video now & have been.