Hi! Make sure that there is water still inside of the filter. You may need to take a small glass or something to pour a little bit of tank water back into it. I've noticed that with my filters sometimes the water will drain all the way out when the power goes off, and other times it doesn't.
If that doesn't help you may want to try to re-seat the impeller assembly. All this is, is the tube that comes up from the tank and goes into the filter. Just make sure that it is pushed down all the way.
Good luck!