We have a lot of trouble with our dishwasher since we have hard water for two or three months a year. This is what the dishwasher repair guys told us to do: FIRST, IF YOU CAN, TAKE THE MACHINE APART AND CHECK FOR BROKEN PARTS. You do this from the bottom. IT IS A LOT EASIER THAN YOU THINK. Replace what you can. Check the motor and all belts. He told me to buy a gallon of MURADIC ACID.(I cannot remember how to spell that name.WE USE IT IN THE TOILETS TO REMOVE THE HARD WATER BUILD UP.Ask some guy at the HARDWARE STORE.HE WILL KNOW WHAT YOU ARE TALKING ABOUT). Use one cup of acid. Pour into the dishwasher. RUN THROUGH TWO CYCLES. THIS DOES WORK, but if you have exposed metal, the acid may hurt it.
From Stella at http://recipecircus.com