I have a Sony Vaio VPCEB24FX laptop that will wake up from hibernation at random times on its own. It will be hours after I put it in hibernation. It has Windows 7 64-bit. I tried the command prompt suggested in other answers but all I get is this message:
Wake History Count - 1
Wake History 
Wake Source Count - 0
If I shut down the computer it stays off. As for waking up from "sleep", I don't know because I don't use it; just hibernate.
I noticed this starting right after the first time I used Windows Media Center. I have gone through the program and can't find anything that would wake up the computer from hibernation. It still happens when Media Center is shut down completely.
Edit: I tried the solution in this answer but there isn't an option like that to uncheck. All it has is the following: