If your disposal is humming but not moving, it is jammed. Jams in the disposal happen when debris such as fruit pits or hard pieces of food become stuck under the blades, preventing them from moving. If you hear a hum, turn off your disposal immediately, or you could burn out the engine. Next, unplug the machine and go under the sink. Look for a hex screw and accompanying hex key, which is usually attached to the side of the disposal. Turn the hex screw in both directions until it freely moves.
If your disposal is running but not grinding, the blades are most likely broken. While you can remove the disposal and take it to an appliance store for repairs, it will be expensive. It is generally more economical to replace a garbage disposal with a new one when the blades break.
If your disposal will not drain, but it is running, that means there is a clog somewhere in the piping after the disposal. Putting vegetable peels or corn husks down the disposal is usually the main culprit for such clogs. Put some baking soda and vinegar down the drain, and let it work itself in for 30 minutes. Next, cover the nondisposal side of the drain with a plug or wet rag, and plunge the other side. Give it a good 20 to 30 plunges before you give up and call the plumber.
When a disposal grinds poorly, it's usually due to either insufficient water or dull blades. Whenever you run the disposal, run cold water at full blast before, during and for 30 seconds after the disposal is running. Also, sharpen the blades once a month by running 5 cups of ice down the disposal. To disinfect and deodorize the unit, squeeze a lemon into the disposal while you are running the ice through it.