I have a big problem with my home theater PC that runs Windows 7 64Bit. Normally, I send that PC to hibernate every evening, but from time to time, it keeps waking up for no obvious reason, and stays on until I realize, which is sometimes half a day later :(

I have already checked for Windows update, which is not set to automatical, since I prefer installing updates manually.

When I look in the system event log, there is an entry called "Power Troubleshooter" which tells me that my system was reactivated at a specific time, but it also says:

Source = Unknown,

which is the most annoying part. So how can I actually figure out, which process reactivates the PC?

Is it possible to set a group policy which forbidds applications or services from scheduling tasks that allow waking up from hibernate at all?