The image on the screen is very dark after the laptop fell off the desk. You still can see the desktop background picture and icons if you look very closely but the screen has no light.
1. Video cable got disconnected from the screen inverter board.
2. Damaged backlight lamp inside the LCD screen.
Possible troubleshooting steps and repair solution:
1. It’s possible the screen is very dark because the video cable got disconnected from the screen inverter board. As a result, the backlight lamp gets no power from the inverter board and remains off even when the laptop is turned on. Disassemble the display panel and try reseating the video cable connectors on the inverter board.
2. If reseating the video cable connections doesn’t help, most likely the screen backlight lamp was damaged when the laptop fell off. The backlight lamp is located inside the LCD screen and it’s very hard to replace just the lamp. I would suggest replacing the entire LCD screen which comes with a new backlight lamp.
By the way, you still should be able to use the laptop with video output on the external monitor.