Have you checked the waste pipe to the outside drain to see if it is blocked? If it is okay, the pump is either blocked by a particle of dirt or grit, or has "Passed-away".
Pour some water into the machine.
Switch the machine to "drain".
Switch on and listen for the normal whirring/humming noise and note if any water is coming out of the ribbed outlet hose.
If no noise is heard when machine switched on and no water is forthcoming the pump is more than likely banjoed and needs replacing.
Davy Mac, March 2009