Windows only: If you've ever come back to your PC and noticed it was rebooted, you might be curious to know exactly when it was shut down, and the Guiding Tech blog has a quick tip to help.
To figure out when your PC was last rebooted, you can simply open up Event Viewer, head into the Windows Logs -> System log , and then filter by Event ID 6006, which indicates that the event log service was shut down —one of the last things that happens before a reboot. This technique won't help you figure out when there was a power outage, but you can filter by Event ID 6005 to see when the system was last turned on — that event shows when the event log service was started again.
It's a simple tip, but could come in handy if you come back to your PC and want to figure out whether Windows Update or somebody else restarted your PC in the middle of the night, or you're just curious how many times you've rebooted in the recent past.
How To Know the Last ShutDown Time Of Your Windows PC [Guiding Tech via TinyHacker]