The vertical lines are most likely due to connections with the data ribbon leading to the screen.
I've often seen it happen to units that were left in hot cars or attics.
[http://www.retrofixes.com/2013/07/fix-vertical-lines-in-gameboy-screens.html|Here's a great guide], from RetroFixes.com, that will, hopefully, help return the screen to normal ...
Once you have the unit apart, you'll be able to line up the screen again. Just be sure to verify that it's straight before completely screwing it back together.