It may be that the lcd is broken. I don't know if there is a way to fix it other than replacing the screen but I am certainly no expert. This happened to my phone and laptop. I had to replace my phone and still use the laptop very carfully. Whatever you do DO NOT put pressure on the screen if it is the lcd it will simply make the lines longer and destroy the display even mor! I've never had it start from the middle of the screen but it sounds like a lcd. Hope you get it figured out and that I was able to help!
In the middle of your computer screen? Part of your screen is dying.
you may have cracked it
It is getting bigger
