I recently updated my workstation from Windows 7 to Windows 8 Pro. After the upgrade, the computer seemed to wake up by itself from hibernation daily (I usually use hibernation instead of system shut down to preserve the state of all open applications).
I have set up all devices (specifically, the mouse, keyboard, and the network card) to be unable to wake up the computer in Device Manager, and have also configured the current power plan to Disable waking up the system on timed events (from the administrative advanced settings section). But apparently these were not enough.
Today I noticed that the waking happened around 4 PM (I was working on a notebook at the next desk). Armed with this information, Ioana has finally discovered that a task called Media Center Update was scheduled to run every day at 3:58 PM, and it had the Wake the computer to run this task checkbox set. Hopefully, unsetting the checkbox would eventually get the problem solved.
If you have the same issue and want to get to the scheduled task settings on your system, follow this path: Control Panel, System and Security, Administrative Tools, Task Scheduler (running as administrator), Task Scheduler Library (from the left tree-view), Microsoft, Windows, Media Center, mcupdate_scheduled, Properties (in the context menu available on right clicking).
Update: It seems that was it! One day after, the computer hasn’t waked up by itself again.
Sorin Dolha's Blog 
Thank you for providing, what should be, the answer!
This had annoyed me since installing W8, I had already changed multiple settings but couldn’t find what was waking the PC. Mine was doing this overnight and had just done it this evening at 8pm, looking at the times for the media center update running they seem to match.
I’m guessing ‘mulţumesc’ is right!
Mike
You’re welcome! (“Cu plăcere!”) 🙂
OK, my PC had been fine since my last post but over the last two days I have again found it running after leaving it in hibernate! I’ce checked all of the scheduled tasks and none of them are set to wake the PC, looking in event viewer a few things ran after boot-up, such as windows updates, but these seem to be tasks which have missed their allotted time and run on next restart.
I’ll give it a few more chances then have to dig a little deeper….again!
Mike
It’s possible that the time configured for the Media Center Update task is variable, probably depending on the time of day you actually installed Windows 8 at!
Yes, i think it is.
Commands “powercfg –devicequery wake_armed” and “powercfg – lastwake” do not help to find this problem.
Media Center scheduled itself to wake up laptop at 2:39PM even from hibernate and even when laptop is in the bag that becomes an oven as it happens – dangerous thing for HW.
Though it was scheduled to disturb computer on the day time it actually was waking it up every night making me to suspect VAIO services that likely did not comply with Windows 8 setup after update. It would be great to know the program which was able to find all violent setups like this one in the computer.
I would not find it by myself.
Thank you very much, Sorin!