Assuming you are using a good quality detergent. And the upper spray arm nozzle is not clogged with mineral deposits, etc.
If you have 2 (or more) spray arms. The upper spray arms are most likely not expelling liquid.
Determine if your upper spray arms are supplied dishwater through tubing that goes up the back of the dishwasher or if the lower arm has a center output (possibly it may look like a collapsed accordion like piping is in the center.
For piping going up the back of the washer the upper basket arm should have a pipe going to the back of the washer. This must meet up properly so that when the water is expelled from the pump it is forced thru the connection and out the upper spray arm (s). If the connection is not made then the water may be partially going thru the upper spray arm or not at all. (Our current washer the connection got moved out of place. But it was easy to move back into place. (Also as prior by Dan check for debris such as cellophane wrapping that loves to get under the lower strainer but not get cut by the grinder resulting in blockage.
Finally if you don't have piping going up the back of your dishwasher you most likely have a series of partial tubes in the center of the lower washer arm (there may be an extending portion up thru the lower dish-rack. It's important that nothing obstructs the flow of water at this point and that the partial tubes aren't stuck together or otherwise obstructed (when water is forced thru them they push upwards and each subsequent cone tube is slightly narrow at the top than the bottom which forces the next smaller tube further upward until it meets with the upper washer arm inlet. here make sure that there is no debris in the inlet which should be right on the bottom of the arm. also the one we had most recently had a rubber gasket that was needed to complete the seal.