Lee Schierer McKean, PA
Since the door is opening, most likely you are not getting good water flow through the pump. This can be caused by gunk (technical term for garbage) in the intake screens for the pump or clogged spry nozzles. The lower spray arm is easy to check as it usually had a large nut that screws off so it can be cleaned. Look at the openings to see if they are clogged. Also make sure it is free to spin when you put it back on. Check the pump performance in mid wash cycle by suddenly and quickly opening the door. You should see water every where inside. Check the strainers around the base for food debris, container labels etc. Most likely you will find clumps of stuff.

Finally, check the water temperature. If the water is too cold the pellets won't dissolve.Your water should be at least 140 degrees inside the dishwasher. It may be a sign that your hot water heater has failed.

Lee