Just follow these simple steps:
=> Goto Run and type eventvwr.msc in the Run dialog box.

=> Events are stored in three log files: Application,Security, and System. These logs can be reviewed and archived.

=> For our purposes we want the System log. Click on “System” in the left-hand column for a list of events.

=> Look for a date and time when you weren't home and your computer should have been off.

=> You can also use this log to see how long someone was on the computer.

=> Just look at the time the computer was turned on and off for that day.

You Are done.