Yes, use a spudger on the panels that cover the controller handles. This shouldnt require to much force and just work your way up to the top. After they pop off, there will be four security T8 screws visible at each corner of the handle. If you are not familiar the screwdriver requried is not a normal T8 it must have the hole in the middle to match the screws. After removing the screws, there is another hidden behind the battery. It is under the sticker which i assume will void the warranty although i am not 100% on that it just seems logical to me. After this screw is removed the back and front should come off
I had the same problem after I took my xbox one apart. I then took it apart again to find a problem and the cable that comes out of the WiFi card was loose and after reconnecting it I have had no problems. I don't know if the problem will be the same with yours but I think the controller signal comes from the WiFi card
Try following this Xbox support guide if you have not already: https://support.xbox.com/en-GB/xbox-one/kinect/kinect-sensor-not-recognized-by-console However i am not 100% sure this will fix it. If it does not it sounds like you will have to send it off to Microsoft for repair.
The blue, green and red cables are for HD only so will only work on YPbPr channel. Also make sure the switch on the end is HD if you are using green, blue and red or TV for red, yellow and white. Or try using an HDMI cable and switch your TV to the corresponding HDMI channel.