Sub not working but amp powering on?

I'm don't exactly follow your description but double check the wires that connect the speaker to the speaker box. If you took the sub out of the box it's possible the wires didnt get retightened or may have come loose. Speakers have large magnets and magnets are very brittle. The drop should not have effected the magnet or speaker structure but look over very carefully and make sure none of the wires on the sub itself are loose or dangling( the wires that actually go to the magnet and voice coils.