This could be caused by several problems including: a bad power cord or power receptacle in your home, a broken or faulty sensor, or a faulty electric A/C motor.

The humming sound indicates that the motor is energized but mechanically blocked. This may have several causes: (1) The shavings holder is overloaded to the point where the shavings are obstructing the cutter blade; (2) A foreign object has become jammed in the cutters; (3) Previous overloading has blocked the cutters. To resolve (3), unplug the sharpener and remove the shavings receptacle. Then, use your hand to tap the sharpener while holding it over a garbage receptacle. If the problem is still not resolved, then unplug the sharpener, turn it over, and use a paper clip or other small tool to clean around the cutter.

This is probably due to a dull or worn cutter or a foreign object being jammed in the pencil bore. To fix this problem, you’ll need to replace the worn or dull cutter blade or unplug the sharpener and try using a narrow tool (e.g. a paperclip) to clear the pencil bore.