Common problems include a unit that has something stuck in it (that's where that dime went), leaking water, or just decayed and worn out.  
If disposal is jammed try forcing the blades back and forth with the hex tool supplied with the unit when new.  To do this insert the hex wrench into the bottom center of the unit and rotate back and forth.  If you do not have this tool a broom handle placed into the top side of the unit may work.  If neither of these work the unit may have to be removed to dislodge the jam.  Remember to unplug the unit before working on it.  Also, the red reset button on the bottom may need resetting if it was tripped due to the problem.  
Service call to repair a jammed disposer: $95.   
Replace garbage disposal you provide: $95
Cleaning Tip - once a  month, with water running thru the disposer, slowly place 2 - 3 cups of ice cubes into the disposer while it is on.  This will help clean it out and keep the blades sharp.  Keep fingers OUT OF OPENING.  
Cleaning Tip
Garbage Disposer
INTERNET SPECIAL: Badger 5, 1/2 hp disposer by Insinkerator.
             Installed: $225 
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Insinkerator's Evolution garbage dosposal.  It is a solid upgrade from the standard units most houses come with. 

YPH highly recommends . . .
1/2 H.P.
3/4 H.P.