The cleaner unplugged it
I remember once client screaming and cursing me over the phone threatening all forms of abuse at me because one of his systems was down and if I did not do something about it now there would be legal action, I'd be sued for lost revenue etc, etc, etc. So after a 2 hour drive to his office I walked in, looked at the computer and then plugged it back in and powered it up. I then just turned and stared at the client.
I then I sent his boss an invoice for a half day, emergency onsite maintenance with expenses with "Problem" filled in with "System unplugged" and "Resolution" filled in with "System plugged back in"