How can i fix my Diplomat ADP8332 Dishwasher?

I have a Diplomat ADP8332 dishwashwer which is not washing properly. I have cleaned the filters & spray arms, checked it has enough salt & rinse aid & have retried with only few dishes in to check it is nothing to do with overloading, but to no avail. There are no lights flashing or codes lit to indicate a fault but each time i load the dishwasher and it completes a cycle the dishes are just as dirty and the powder dispenser is open with most of the powder still in it! Water is coming through but i am not too sure how much. I am at a loss...any suggestions before i surrender and pay for someone to come and fix???