Not sure I follow. If just the LCD-Panel's Backlight is turning-off (use a flash-light) then replace LCD Panel. If the whole LCD Panel is temporarily turning-off (but machine still works with External Monitor) if might just be a bad "lcd-panel to motherboard" cable. Yeah, they eventually go bad with all the bending in the hinge. If something else, likely a major hardware failure (like motherboard). Better to have a qualified computer technician take a look at it. 
Hi I can't seem to figure this one out. The screen for my girlfriend's XPS 13 9350 randomly turns black (dim black light) but the laptop and the keyboard light stay on. After some time - anywhere from 10 minutes to 6 hours - it comes back. I've tried BIOS updates, driver updates, all the updates available I could find at Dell, removing and reinserting the RAM stick, as well as the battery. I'm having trouble because the problem is not repeatable and occurs randomly. Should I look at replacing hardware?
XPS 13 9350 Intermittent Black Screen