Often when a garbage disposal is broken, it's usually actually not. What has happened is that something got stuck in it and stopped the motor from turning, and then to prevent things from getting worse, a fuse blew.
Secret number one is that disposals will often have their own fuse, and a small button on the bottom of the device itself that will reset it. If this is tripped then you may feel a small click the first time you press the button as you reset it. If there is no button or if it's broken (OR WORSE, TAPED DOWN, JESUS CHRIST) then you might also have to check the circuit breaker box for your apt/house.
Secret number two is that there is often a hexagonal hole in the bottom of the disposal, right in the center, and that if you find the right allen wrench you can use this to turn the motor manually. It will help dislodge things that are stuck in there, and when it turns freely in both directions you can know for sure that the thing is not obstructed.
You can do a quick check by resetting fuses, trying to run the garbage disposal, and listening for a quiet hum and/or checking if the fuses got tripped again. This will not fix anything, they are just symptoms of the real problem...
I know it's gross but you have to reach in from the sink and remove everything you can find with your fingers. If this makes you nervous, the disposal is probably plugged into an outlet and you can just unplug it, or you can tape over the switch, or if you know which circuit breaker belongs to it, turn that off. Then try the allen wrench, then reach in and pull out anything you can find, then try the allen wrench, etc.
When the allen wrench can turn the disposal freely in either direction, you have found the real problem and removed it. Check the fuses again, and then try to run it for real. If it doesn't work now, it's probably truly fuarked, I dunno I'm not an electrician, but I have "fixed" several disposals myself this way.
If you do this and it works please report back about what you found stuck in there. So far I have found a delightfully mangled penny, olive pits, and the plastic tube from a tip of caulk.