Make sure your power supply is capable of driving two motors.
Replace the motor's with LEDs if that works then the code is fine and it is the interference caused by the motors that is stopping it working, add more supply decoupling.
Make sure your power supply is capable of driving two motors.
Replace the motor's with LEDs if that works then the code is fine and it is the interference caused by the motors that is stopping it working, add more supply decoupling.