A few days ago a black vertical line appeared on the top left corner of my screen, about 3 inches long. It's not a hardware problem, as it appears on my TV as well when I connect my mac to my TV. It hides everything behind it and sometimes makes that area look distorted. It even shows in fullscreen mode in movies. I have a mac air 10.9.4 I've been using Final Cut Pro X and I think it started around the same time; I read somewhere that it might be a graphics problem, but no solutions. I took a screenshot, attached below, though not sure if it shows here. Thanks in advance for your help.