My Computer is showing logins and time changes in the middle of the night.

Recently I yelled at my son because it appeared he was logging into the computer late at night and changing the time and doing other activities.  He swore he wasn't and I believed him.  I started monitoring his bed behaviors closer.  I also started asking him to turn off the computer before going to bed at night in hopes it would stop this strange activity. It hasn't.  Even though my computer is off, it's showing him logged in. Even during school hours!

The curfew monitoring is still showing him signing in late at night when I know he's not.  Is there some kind of ghost in the house?  Is my computer getting hacked through web?  I don't know what to do but I want it to stop!

 

I don't use McAfee, I don't use anything but Norton.  Please help me stop this.