how to un-jam a garbage disposer

It can happen to the careful homeowner, the mindful tenant, and even the experienced plumber. You flip the switch to the magic portal in the bottom of the kitchen sink whereby all unwanted things disappear, but it either hums a disapproving groan or protests with a clashing noise as if it's about to fly apart, then silence. If you're lucky, the thermal protection device engaged before the motor windings burned up and went out of this world in a blaze of glory. 
There are two common disposer designs, the Emerson Electric design sold as In-Sink-Erator (ISE), Kitchenaid, Kenmore, and a few other labels, then there are the Whirl-away, GE, and bargain basement designs that sound more like a boat motor than something you'd want in your kitchen. 
Yes, I'm a little biased towards the Emerson Electric design and for good reason. 
The Emerson design has a hole in the middle of the bottom of the motor housing where an allen wrench can be inserted to free up a jammed disposer. 
1. Turn the power off
2. Rotate the motor both directions until it frees up the obstruction
3. Remove the obstruction using a flashlight and a pair of needle nosed pliers
4. Run the faucet while running the disposer for at least a minute and check for leaks through the bottom of the motor housing in case the offending object tore a hole in the bottom plate of the grind chamber.

If the motor is graveyard dead, look for a reset button on the bottom. On and Emerson design, it is a small, square, red button. Press it. If it clicks, try again. If it's still dead, it could be a problem with the switch or power circuit, but most of the time that is an indication that the disposer has "drawn the curtain, shed it's mortal coil and joined the bleedin' choir invisible" - Monty Python, Dead Parrot Skit

The GE and Whirl-away designs do not have the hole in the bottom for an un-jamming tool, so with those you have to use a special un-jamming tool that is inserted through the top. Sometimes a wooden spoon or long screwdriver placed against the rotating plate can be used to free up an obstruction. These have a thermal overload device button like the Emerson designs, but they are typically located on the side of the unit towards the bottom. Otherwise, the same procedure as above applies.

If the disposer is dead, leaking, or cracked somewhere, it's time to replace it. In the meantime, it will clog from continued use since it cannot run and grind food bits, so you can manually rotate it with an un-jamming tool to get by. 

If the cost of a plumber is too much for your budget or you just want to tackle the task yourself, check out my e-book on Amazon Kindle called Dave the Plumber's Handy Guide to Disposers. It is a step-by-step guide on how to replace a disposer with links to exclusive videos so you can learn by watching the Pro at work.