Why is only 3 of my4 motors starting on my promarkp70drone

The P70 Shadow drone has motor protection feature which will shut down power to the motors should they come into contact with an object. You must do a factory gyro reset to regain motor operation. After binding the transmitter to your drone and connecting your devices wifi to view the status confirmation on screen. Simultaneously move the left stick up to the 10 o'clock and the right stick to the 2 o'clock position hold till you hear a beep and the display will confirm gyro reset ok. Before test flight be sure to connect calibrate GPS satellites for a safe return to home flight. If the third motor is still non functional then could be a failed/bad motor. If you ever hear a motor making a loud screaming sound stop do not attempt to fly the motor is going bad and will eventually fail during mid flight and you will severely crash.