You've obviously got some more screwing to do, Michelle.
Is there another similar connector into the back of the monitor, or is it just a lead that comes out? Failing that, er, I dunno! Perhaps take out the one you screwed the other night, and screw it in again? Other than that, it sounds like a loose connection somewhere else, if it happened when you knocked the desk, but Sandra could be right, and it could be inside the monitor.