If you've had your dishwasher a while, and you live in a hard-water area, consider limescale buildup in the works - not detectable in the readily-accessible outflow pipes.  Limescale buildup limits the water-flow and confuses the machine's sensors.  Usually the works are accessed through the side of the machine.  Grit your teeth and hire a local repair person who knows what he is doing.  Much cheaper than throwing in the towel and buying a new dishwasher.
                 Judith
                
 October 2010