Download the video driver, then go to device manager to suspend or remove the old driver, and install the new one... Anything better.
If not, you likely have a defective video graphics inverter or backlight. Not difficult to fix but tedious and time consuming... First, see if you can find the inverter and backlight cheaply on eBay or other supply source. Then look at the dell site for drawings and images of what is needed to remove the old one.
The units just plug in. But there are many screws of different sizes which you must remove from the bottom of the computer, then remove the keyboard, then remove the screw covers... and there can be as many as 16 to 24 screws... it is important to draw yourself a "map" as to where each screw size goes when you reinstall everything.
The most difficult part is removing the screw covers so they can be replaced in a way that is attractive.... then getting screw cover replacements and the correct glue or adhesive.