It sounds like the clay pump motor is bound up...
remove it from the worm gear... test run it like you did in the video and confirm it spins
Then remove the screw from the work gear, attach the motor to the worm gear (not to tight) and confirm the work gear is spinning.
Tighten down the motor, making sure it still spins once your done.
then Reinstall the screw and both flanges... run the motor again to make sure the screw works in both directions...