iPhone 5C display very dim to black even after replacement

I have replaced the screen on my iPhone 5C (have experience replacing screens) as it was black but I still could hear it function. I replaced it with a new screen which hardly displays anything, either black or nothing. So obviously I checked all the digitizer flex cables and the problem seemed to come from the camera sensor cable. Replaced this cable as well. Everything snaps perfectly in the slots, I can't see any damage, but nevertheless, screen is still black or very dark (a little is visible but mostly black). What could I do now?