There are a number of things that may make your dishwater not work properly. For instance; to mend a dishwasher that does not let the dishes come out clean, take out the spray arm and clean it. Then, clean the valve screen and float switch. If the dishwasher is unable to start, you should try spinning the motor using your hand.
How to mend my dishwasher? – http://uk.answers.yahoo.com/question/index?qid=20080116081522AAsjFco