KitchenAid does not spin propellors

We have a Kitchenaid dishwasher that is not cleaning dishes. It fills with hot water correctly, it pumps the water through the bottom rotating propeller and the top one, but neither of them spin. I have tried to test water flow by placing coffee mugs in upside down with a paper towel in them to see if they get wet. The propellors do not spin although some water does flow through them.
HELP!!