Set all wash arm pointing toward you. Start the cycle, when you hear the water splashing inside open the dishwasher and see if the arm have moved. May need to do a couple of times to verify. If they are not moving, look to see if holes in spray arms are plugged. They need flow of water to turn and clean.
Another thing you can do is to put a cup in the top rack right side up and see if it gets filled with water. This will tell you if the pump is pumping water to top arms properly.
Check level of water in tub, in some of the newer units (last 2 years) there is very little water, but older models should have visible water in tub.
If any of these seem not right please call me and let me know what you have tried so far, and we can go from there.
I will be happy to give advice if you are not sure how to do these checks or would like to fix yourself.