Top Arm does not spin so glasses are not...

Make sure the water level is just at or below the heating element. Low water level will cause the pump to "run out of water" before all wash arms and connecting tubing are filled. A pulsing sound during the wash cycle will verify. Low water pressure or a bad water inlet valve are one cause. Water siphoning ou the drain line is another. Look under your sink and verify the drain line goes from the garbage disposal or sink tailpiece all the way up to the bottom side of the coutertop enroute to the dishwasher.