Power on your spa. If you hear a humming sound for a bit and then the pump ceases to work it is likely the result of a failed motor. A technician will have to replace the dead motor.
Check the pump area for leakage. If there is leak, look for damaged O-rings, seals or fittings around the pump. These can be removed and replaced on your own with new components available from your spa retailer.
Check the leaf trap of your pump to make sure it is free of gunk and debris.
Ensure the pump primes by filling the leaf trap with water and running the pump to bleed out the air. This is necessary if you have recently drained and refilled the spa as there may still be pockets of air in the system.
Check all valves near the pump and make sure that they are open. Tighten all O-rings on the pump.
Ensure that your spa is filled to capacity. If the water level is too low it could be the reason your pump has low pressure.
Clean the basket around the pump of any gunk and debris.