How can i check why my pc was restarted ?

I came home now and i saw my pc restarted. It was on the log in screen so i entered my user name and password and everything loaded fine. But why and when my pc was restarted ?

What i tried to do so far is running Event Viewer then i went to Windiws Logs > System and then double click on System.
In the window i have some errors but none of them related to system crash or restarted.

I tried to sort by event id and find if there is event number 6006 or 6005 but there are not any of this id's.
The last error i see was few minutes ago:

The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID {D63B10C5-BB46-4990-A94F-E40B9D520160} and APPID {9CA88EE3-ACB7-47C8-AFC4-AB702511C276} to the user NT AUTHORITY\SYSTEM SID (S-1-5-18) from address LocalHost (Using LRPC) running in the application container Unavailable SID (Unavailable). This security permission can be modified using the Component Services administrative tool.






But nothing that tell me why my pc was restarted.

I also tried to go to Control Panel > View last installed updates
The last update was yesterday so it's not the reason why the pc was restarted.

Maybe there was a power fail at my home ? The light are all fine but maybe there was a power fail for some seconds and that's why the pc restarted ?

To find 'when', look in Windows Logs, System for Event ID 12, Kernel-General:

The operating system started at system time ‎2017‎-‎01‎-‎17T18:34:03.492577800Z.

Then look for clues as to 'why' in the immediate vicinity. A power cut would be indicated by Event ID 6008 "The previous system shutdown at Time on Date was unexpected." unless accompanied by event ID 1003 for a BSOD.