Image sensor replacement fixed freezing but now back Lcd won't work!

My Gopro Hero 4 was freezing after about 10-15 seconds and wouldn't show anything but a black image on the LCD. ( I could go through settings and everything just had black image. So I replaced the image sensor and it quite freezing and takes video if I use front screen, but the back LCD appears to be receiving no power because it won't even light up now. Does anyone have any ideas of the possible problem? I checked the 3 power supply ribbons and they seem to be in place.