Power off... Stick a flat screw driver in the motor shaft at the back end of the motor behind the dust cover. Try and see if the motor shaft spins freely and not locked in place/seized. If it is tight.. rebuild the motor with new pump seal and impeller and possibly front bearing. If it spins free.. Power On and wait until the motor is trying to start/hum and give the shaft a spin to help the motor start. If it starts up with a bit of help then you might have a bad start/run capacitor on the motor.