Hi,
Try connecting an external monitor to the laptop's HDMI port and see what the display is like.
If it displays OK then you either have a faulty video cable, a faulty video cable connection at either end (motherboard or screen) or a faulty LCD screen.
If it displays the same as the laptop's screen, then you either have a GPU problem (most probably CPU as they are integrated) or a motherboard problem.
If the problem appears to be'' not ''CPU/ motherboard related, here is a link to the service manual videos which may help you to gain access to your laptop so that you can locate the problem.
http://blog.parts-people.com/category/dell-inspiron-repair-manuals/inspiron-15-3541/