[rmcdonnell]

If the starter motor works and whizzes out of the car, and you've turned the motor over by pushing the car in gear so the teeth on the flywheel should have moved, then I think these are the possibilities:

Wrong starter motor model and dimensions
Not installed correctly in place, not fully home
No teeth left on the starter.
No teeth on the flywheel.
Something wrong with the starter allowing it to spin, before the gear is fully flung out.
Something very bizarre I haven't thought of.

cheers
Rissole.