This is going to sound really crazy, but is it's one of those screens that you can touch and see the trace of your finger? If it is, try to actually "tap" on the line with your finger and it might disappear. If it's a hard screen, I'm not sure if that will work or not. Yeah, I know it sounds super nuts, but I had a tv screen that had a line and after tapping it like another individual suggested to me, it went away and I was left floored. I thought my pixels were going bad and that I needed a new tv.