Had a similar issue recently with my Forester. This is just a possibility, but it's simple to rule out. There is a little flange on the back of the starter that a connection slides over to allow the engine to start. On your car because it's a manual it's connected to the clutch pedal. If that is not connected then the ECU assumes that clutch pedal is not depressed and will not allow the car to start. On an automatic it's connected to the neutral safety switch on the transmission. It will immobilize the vehicle if not connected. Best of luck.