I was having the same problem -- after updating the firmware on both the controller and the aircraft, nothing was recognizing each other. RC had solid red light LED light and the aircraft had flashing yellow lights. Found the solution in a video in the DJI Go app.
Hit the Menu button in the upper right, then Academy, then Video Academy, then watch the "Linking the Remote Controller" video.
I'm trying to re-watch the video but the app keeps crashing on me. Basically it will have you power it all up (RC and aircraft), then connect the app to the controller. At this point, the app was showing me "How to Connect" and not recognizing the RC or the aircraft.
Now do the C1 + C2 + Record button combination, then you should hear a beep. Now press the ISO wheel in (the wheel on the right rear side of the controller. Now the LED on the RC should turn light blue, indicating that it is in linking mode. Now, you have about 60 seconds to use a paper clip or pen to push and hold the Link button on the aircraft. This is a small button on the right/starboard side of the aircraft (if you're looking at the aircraft from the rear, behind the camera. If you're looking head-on at the camera, it would be on your left side). It is next to a flashing red LED, to the left of the micro USB slot on the gimbal.
If you hold that guy in, it should all light up and start working. I wish I could watch the video all the way through and have a little more confidence in the recap above, but the stupid app keeps crashing, and the videos I'm finding on dji.com (outside of the app) aren't the same as the one that led me to the promised land.
