Backlight works but no video - external display works fine

Hello there,

I have a Carbon 4th gen (Type 20FC), with WQHD display, a lovely device, but recently it developed a problem.

When turned on, there’s black screen. Backlight is working, laptop boots up just fine (confirmed on external monitor via hdmi). I have tried 2 new cables for the LCD, still the same. Once it beeped two times (indicating display/RAM problem). Any ideas?