One of our Reference staff on the same Saturday watched a teenager bugger up a CDROM drive. She said she didn't know how he had done to it, but thought there was a library card inside the drive. Sure enough I have just fished a library card out of offending CDROM drive which was preventing the drawer from closing.
Finally, in response to an email that "the mouse on PC 5 is not working..."
"Have they stolen the mouse-ball or is the breakage something more fundamental than that?"
"No, that's the first thing I check! The up-down movement works on the bar inside, but not with the ball in it; I tried to 'roughen up' the ball, without success."