Help me find the offending process waking my Windows 7 PC from hibernate every night

That sounds like the Windows Updates.

"Interestingly, my Windows Updates are set to check at 3am. The first event I see in the Windows System event log is always around 3:15am and it's the system time being checked. There is an event in there from the Power-Troubleshooter service that indicates the PC has awaken from sleep (really hibernate in my case), but indicates the Wake Source is ""Unknown"", which jives with powercfg.

I will move Windows Update from 3am to 6am to see if that's it, but even if it is, it wasn't causing the problem for the last 6 months. Maybe a Windows Update. I thought it might be related to NIS 2010, but cannot see anything scheduled by that program or any other in Windows Scheduled Tasks that is running at that time.

As far as wake on LAN in the BIOS, it's probably set if available, but the network card is explicity set to not wake from sleep in Device Manager."

"I had the exact same problems with the exact same symptoms. I looked at the scheduled tasks and did not see any task that was configured to wake the system up for execution.

I started Google Updater and configured it to never update Google software.

Since then the system has not woken up by itself. Its only been a day, so it may have been a fluke. If it works in the long run then it obviously raises the question of why would Google updater wake up the system when it was clearly configured not to do that in the scheduled tasks."

I had a similar problem, and discovered the culprit: after being asleep for 6 hours, my computer wakes up and goes into hibernation. Since my computer usually falls asleep shortly after I go to bed, it kept waking me up when I was in the middle of sleeping. More here (including instructions on how to disable).