The pump may have stopped circulating because the water level in the pool/spa is too low. If the water level has dropped below the center of the skimmer, air may get into the system causing it to stop working well. "Re-prime" the pump by raising the water level in your pool/spa, then remove the pump lid and place a few gallons of water in the pump basket. After reattaching the pump lid, open the valve under the pressure gauge on top of the filter. Turn your equipment on and when water sprays from the open valve, close the valve. The equipment should re-prime itself. You can tell the pump is working when the pressure gauge moves.