It's the screen itself. Changing a cable is not going to help this situation. It's either a defect with one of the screen's internal bulbs (not worth replacing -- replace the whole screen), or often the metallic tape on the back of the screen comes loose or becomes warped or somewhat "rippled" due to liquid, causing light to "get out" and cause darkness in the areas where the tape has pulled away. Sometimes if you take the back of the screen casing off and can spot this waviness of the tape, you can tape it down again and reduce the problem, however, I don't think I've ever succeeded in eliminating it completely. You're going to have to go into the screen casing anyway, so it might be worth trying, but I suspect you're going to need to replace the screen if your goal is to once again have a perfect display.