Once in a while the garbage disposal gets jammed. This happened to me today, so I did what my dad taught me to do: get the broom! Place the end of the broom handle (a wooden broom handle works the best) in the garbage disposal at an angle so that it fits snug against the rotors (or whatever they are called - you know the metal parts that turn and grind the food). Next, turn the broom handle so that it forces those rotors to move. Most of the time I cannot tell that anything happened, but I stop and try the garbage disposal and nine times out of ten it works again.
One other thing to remember about garbage disposals (also from my dad) - and this will make yours last longer - whenever you run it, always run the cold water also. This helps to keep the motor in the garbage disposal cool and forces the ground up food through the pipes faster and more efficiently.