If you hear humming with the switch on the thing is probably siezed by junk in the cutter. If so, insert the proper size allen wrench in the bottom center of the disposer and turn it one way or the other to see if you can free it. If no motor hum, check that circuit breaker in the household electrical panel hasn't tripped.

My Kitchen Aid garbage disposer does not come on. I pushed the reset breaker button on the side of the motor, but nothing happens. can this be fixed, or do I need to purchase another one?