Windows – How to tell what wake source is when Wake Source: Unknown

I had the exact problem like the OP, Win7 32Bit, PC hibernation and it woke up at 3:57am precisely every night, but there was nothing noted in the log and the powercfg -lastwake gave no information.

The problem was the Windows Media Center. Once, I even caught it red-handed downloading some updates right after the PC woke up, so I disabled the auto-update in the settings. So when the problem persisted I wasn't thonking of the WMC as the culprid anymore.

But it turned out that even though I turned it off within the WMC, the task within the Task Scheduler was still up and running. To disable the task simply open the Task Scheduler, navigate to Task Scheduler Library\Microsoft\Windows\MediaCenter. There should be the mcupdate_scheduled task. Disable it – problem solved!

The "Wake on Magic Packet" option may turn the computer on (if someone/something is pinging the computer). Go through Device Manager to resolve this and not the Network and Sharing Center (see EXPLANATION below).

STEPS:

1. Open the "Device Manager"
2. Open the "Network adapters" tree
3. Select your adapter (you may have two if you have both wireless and Ethernet capabilities)
4. Right-click on the adapter
5. Select "Properties"
6. Select the "Advanced" tab
7. Under the "Property" box, scroll down and select "Wake on Magic Packet"
8. Change the "Value" drop-down box to "Disabled"

EXPLANATION: You can go through the "Network and Sharing Center" by selecting "Change adapter settings" on the left side of the screen; selecting your adapter's "Properties"; selecting "Configure"; and then going to the "Power Management" tab. However, I've noticed on some of my computers (including Windows 7), that the magic packet option will be grayed out or unchecked in the "Power Management" tab but be "Enabled" in the "Advanced" tab.

Using the Device Manager route solved my issue with unwanted waking from sleep on my laptop. Good luck.