Quick test, see if your wiring harness is even functioning. With the gun fully assembled, take out the motor. Hook the leads up to the motor, make sure the motor is secure (you can hold it in your hand, DO NOT touch the pinion gear you will end up with a hole in your finger, hold it by the sides), flip the safety off and pull the trigger.
If the motor spins up, you have a seized gearbox. Take it to JT and have them look at it.
If the motor does not spin up, you have a malfunctioning wiring harness. Take it to JT and have them look at it.