When attempting to start the drone via a CSC, the rear LEDs flash RED four times, then stop and the motors do not start. The last flight ended with no problems - no crash, no hard landing. The manual's troubleshooting does not list any error code for such a display. Visual inspection shows no unplugged cables or obvious external damage. Any ideas? Plugging into a PC and running Assistant is out, as the USB port on the drone body is not functioning. If it comes to this, on previous problems that needed expert repair I sent it to Drone Nerds in North Miami, Florida and was satisfied with their work. Anybody want to recommend a repair shop they've with which had good results?