well I would start with what I know, batteries are full in both units ?....I think you've flown this combo before, did anything happen since your last flight, maybe a "light" crash , radio (controller) get "bumped" off the kitchen table? it doesn't take much for a pcb to break a connection just to ruin your day. Without turning screws and opening anything up (not recommended) their are only a couple things it could be, I would start with the batteries