Problem Hibernating

Hi i have a hp laptop, and all of the sudden whenever i try to hibernate it, it says its hibernating, then when it seems to shut off, it immediatly restarts again. Any ideas why it wont stay off? I changed some of the power settings before it started doing this, but only the amount of time it should take to hibernate when plugged in, if i dont use it. I said 5 hours because i was downloading something, but i didnt want it on all night. this shouldnt affect it when i manually hibernate it though, should it?
Oh, and if i shut down the computer it stays off.