My Computer is not working

My favourite definition of the problem.
In this particular case, the DU (Dummest User) had told me a few days before this call that he knew how to program computers...

Here's the story:
DU: My computer is not working.
Ad: Could you be a bit more specific?
DU: It's showing nothing on the screen.
Ad: Aha - that sounds bad - coming over...
<Admin walks over>
Ad: So, show me what you did.
DU: I switched the computer on...
<At which point Admin internally breaks into hysterical laughter>
Ad: Try pushing the other switch, the one on the PC - not on the screen!
DU: Didn't know that...

Yeah - great programmer - only needs an Admin to switch on...