Computer Alarm clock programs?

hey guys i know there are tons of alarm clock programs for computers but is it possiable to have one that turns your computer on at a certain time? becuase my computer is really loud and heats up my room and id rather leave it off at night. but i would love using my pc for wakeups because 5.1 surround sound would mean i would acutally wake up on time lol plzz help guys or i guess even hibernate would work if possiable.