I usually leave my computer on all the time and just restart or turn it off once a week. I've heard its bad to turn it off or restart a lot, kind of like stop-and-go traffic with a car. But I don't believe that would have anything to do with your problem. As someone above mentioned open up your case and clean EVERYTHING off, get some canned air and spray out the dust and take a q-tip and clean off the fans. If yuo can, while your computer is starting up, hit DEL or whatever to bring you to the BIOS and see if yuo can't see how hot your processor is running. It shouldn't be any hotter than 110 fahrenheit. If it is you'll probably have to look into investing in some better fans or some more heat sync for your processor.