I just got my Phantom 3 advancedtoday in the mail. it has been used so it is not brand new. When I turn it on, the indicator lights are solid red, and blinking yellow. The app connects to the camera but the drone will not respond to the controller. I have just downloaded the firmware and started the update but, the camera light is just solid green. the LED
s are still blinking yellow and solid red. I'm not sure whats going on but I don't know how I can fix it because there is no error message or anything telling me what might be going on. Before I even started to install the update the app said everything was normal, but it says that RC signal is lost. It also switches back and forth to Atti mode which I'm not sure what thats about either. Any advice?

The red lights indicate the front of the drone.  The blinking yellow lights are a status indicator of no GPS signal and normal for inside the house.     Have you had it outside yet so it can get a GPS lock?    You also need to calibrate the compass.    Have you read the manual?   When you say not responding to controller, what are you doing that makes you think that?

Is it a slow blinking yellow or fast? What firmware version do you have on the aircraft and RC?

First I would suggest you get a manual and read it if you didn't get one with it you can get one online second there could be a number of reasons in no order try resetting the the craft and RC after ther firmware update ,you can try calibrating the craft , try switching the RC on first then the craft,you can pair the craft and RC again ( instructions in the manual), take it outside way from all metal and electrical interference and try reconnecting from the list try the obvious ones first is that don't require a manual hope I'm right here but I'm sure someone will advise better qualified than myself

Thanks everyone. Finally figured it out. Updated successfully and works great. Thanks!