I am having a similar problem with my dishwasher. I am going to use this checklist that I just found. Perhaps it will help you. Good luck!!
Check sink drain and drain hose for restrictions
Unjam the motor
Unjam the pump
Check the drain valve
Check the drive belt
Test the timer motor
If you have a brand new dishwasher or garbage disposer, check the knock out plug on the garbage disposer
Sheila, January 2005