First look for a button on the bottom. It is usally red but could be black. Push it in and try the disposer. If it turns on but hums, then turn it back off and see if yours has a hexagonal socket in the middle of the bottom. If so, use a 1/4″ allen wrench to twist it back and forth until it moves freely then turn the disposer on again. If it runs and makes a lot of noise or stops immediately, there is a foreign object in it and you will have to use a flashlight to find it.