The motor is "humming" so why aren't the blades working?
When I insert a pencil into the sharpener I can hear a "humming" noise, but the blades don't seem to be working.
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.