Is the end that goes into the wall in firmly?
Do the rest of the things plugged into that outlet work or might a circuit breaker have popped?
Is the outlet that it is plugged into a switched outlet (one of the places you plug into is connected so that the light switch to the room has to be turned on for it to work?
Is it plugged into a surge protector and has the off switch on the surge protector bar accidentally gotten turned off?