Motor is damaged and the armature is rubbing against the magnets. Disassemble motor and see if the armature can be realigned by reassembly. Motor may have to be replaced. Motor has been running, then fails to start. Replace the fuse or reset the breaker.
Armature is shorted or went to ground.
Motor may make a humming noise and the circuit breaker or fuse will trip. Disassemble motor and inspect the armature for a burnt coil. Inspect the commutator for burnt bars. If this condition exists, the motor needs to be replaced. To test, set your OHM meter to the RX1 scale, touch probes to bars 180 degrees apart all around the commutator.