Go to this Web page, it will give you detailed info about syncing the controller to the craft and what the l.e.d lights on the controller indicate. Phantom 3 Professional-Remote Controller - DJI Wiki
Without more detailed info it will be hard to diagnose. Is the tablet telling you you have no visual feed or is the controller first led stay red when both the aircraft and controller are both on?
Going to need some more information. First which update are you on now, and which one did you come from. Did you do the updates in between and have you updated the controller through the dji go app on your tablet?