If the disposer is jammed, you might hear a humming noise when trying to turn it on. Turn the disposer off right away, then unplug it from the wall socket (or at the circuit breaker). Most garbage disposers have a port at the bottom, which you can use to insert a 1/4″ Allen wrench (usually supplied with the disposer) and free up the disposer by turning the wrench back and forth. With the power still turned off, remove any foreign objects from the disposer, then push on the red button (located near the port, at the bottom of the disposer), in case it has popped out, to reset the disposer.
If your disposer does not have a port at the bottom, or if you can’t turn the wrench, you might have to call a professional or replace the garbage disposer.
