The lower part of the laptop screen displays horizontal lines running from left to right and flickers. Moving the screen makes the image better or worse. The top part of the screen displays the image properly. You’ve tested the laptop with an external monitor and the external video appears to be normal.
1. Bad connection between the video cable and motherboard/LCD screen.
2. Bad video cable.
3. Bad LCD screen.
Possible troubleshooting steps and repair solution:
1. Try reconnecting the video cable connection on the motherboard.
2. Try reconnecting the video cable connection on the back of the LCD screen.
3. Try replacing the video cable with a new one.
4. Try replacing the LCD screen with a new one.