Flip the switch and hear humming? Motor is trying to spin but something is stuck. Hear nothing? The thermal overload already tripped. The jam is almost always something hard or fibrous wedged between the impeller and grinding ring -- bone, fruit pit, utensil, bottle cap, or a wad of celery or corn husks. Every disposal has a hex socket on the bottom for a 1/4-inch Allen wrench. Insert, turn back and forth, free the impeller. Five minutes, no plumbing knowledge needed.