Check for:
Not enough water.
Clogged drain line.
Disposal isn't grinding finely enough.
Remedies:
Run more cold water when using the disposal.
Don't use harsh chemical agents.
Flush with hot water to remove a grease clog, then remove the drainpipe and clear it.
Replace a dull shredder ring or any broken flyweights.
from:
http://www.allabouthome.com/tips/app...chor-The-46919
Also, garbage disposals like 10-15 seconds of water before and after being on. Have you tried the reset button?