The laptop screen shows vertical dotted lines. The dots are red and moving up and down. The external monitor connected to the laptop either has a garbled image or shows the same dotted lines.
1. Failed memory.
2. Failed video card.
Possible troubleshooting steps and repair solution:
If the problem appears on both the laptop screen and external monitor, it’s not related to the laptop LCD screen or video cable. Most likely the problem is related to the faulty memory module or video card.
Download Memtest86+ (google it) and test laptop memory. If the laptop has two memory modules installed, remove them one by one and test separately. If one of the memory modules fails the test, move it to another slot and test again, just to confirm that it’s a bad module, not the memory slot. Replace the failed memory module with a new one if needed.
If laptop memory passes the test a few times, most likely there is a problem with the video card. In most laptops, the video card is a part of the motherboard and cannot be removed and replaced separately. If the video card fails, you’ll have to replace the entire motherboard.