Why does laptop display white screen? (Works with external monitor)

The laptop boots up normally but doesn’t show the apple logo on the screen. The screen is white which must be the backlight as I can adjust the brightness.

I typed in the password and pressed enter to login - then plugged in the thunderbolt cable connected to an external monitor which worked fine.

I can use the laptop normally with an external monitor, (which allowed me to type and send this post) but the display on the laptop stays white.

I removed the screen to replace the LVDS cable and put everything back together which didn’t solve the problem. I’m not sure what to do next, does anyone have any ideas?