You can definitively confirm the fault by running a screen diagnostic - hold D through powerup.  If the fault appears on the test screens (it almost certainly will), the screen must be replaced. If it does not (small chance) then the GPU is the problem, and it's the mainboard you will need to replace.  
I have an issue with my dell Inspiron 3543 I was working on my laptop and then 1 white line appeared in the midlle of the screen as the days went by it multiplied and now I have over 10 lines how do i fix it?[IMAGE][IMAGE][IMAGE]
my laptop screen has horizontal lines in the middle