Please do try these troubleshooting steps that may help.
- First is to test the GPU if it's working properly or not.
- Connect an external monitor and see if the same lines will appear on it.
- If the external monitor will display normal that means the problem lies on the LCD of the laptop.
- I would suggest opening the laptop and check if the ribbon cable is connected properly.
- Unplug the ribbon cable on both ends then plug it back in just to make sure it's seated properly.
- If these will not work the only solution would be to replace the LCD itself.