Hold the D key through powerup to initiate the screen self-test. Does the fault show on the test screens? Yes:  replace the display panel. No:  the problem is elsewhere (internal cable, mainboard).  
Almost half of my screen  of my Dell XPS 15 9510 is becoming darker ( the right side of the screen) as the days go by. I use to have a dark line on the screen, but now almost a third of the screen has become dark and becoming difficult to read from that side. any advice on what I can so to resolve this?
Screen becoming black