Hold down the D key and press the power button to power up the laptop and run the LCD built-in self-test (BIST). That will run diagnostics on the display panel. If the same issue appears during that self-test, then the issue is with the display panel. Parts-People has genuine OEM replacement displays. How to Run the LCD Built-in Self-Test on a Dell Laptop.
When I turned my laptop on this morning the bottom half had a kind of screen of horizontal lines across it. Restarting didn't work. I made sure all firmware was updated. Ran diagnostics. Everything is up-to-date, no problems found. Even, when I tried to take a screenshot to do this post, it didn't show the problem (what I've posted below is a photo of the screen). The laptop/screen weren't physically damaged in any way that I am aware of, but it seems like the problem must be a physical one? Any advice would be much appreciated!    [IMAGE]
Bottom half of display is covered by close horizontal lines