Question Main screen doesn't get turned on ASUS laptop

[ToastyKeycaps]

I have an ASUS laptop G550JK with Intel Core i7-4710HQ, 8GB of RAM and GTX850M 4 GB. Also it is dual boot with Ubuntu and Windows 10. An year ago weird issue started coming up where there was 50% chance that when the laptop boots(cold boot) the main screen wont get powered/recognized by Windows 10, BIOS and GRUB menu. The laptop still worked with external screen though. I would have to reboot machine a couple of times to get the main screen working again. Even though the main screen wouldn't get any backlight in BIOS/Windows 10/GRUB it would immediately start working flawlessly when it reached the Ubuntu splash screen. Both GPUs worked in Ubuntu too. Over time the issue got worse, and now 50% is 100% chance. So I can't use Windows 10 on the main screen anymore only with the external screen. Ubuntu still works weirdly enough. I went to the repair shop with it, and they tried to reset BIOS, that didn't work. They proposed the expensive motherboard swap, which is not worth it.

What the issue could be? And why Ubuntu still works, but the rest doesn't?

 

[hang-the-9]

Could be an issue with the nVidia video card, does your external monitor show it's connected to the nVidia or the Intel video? Or Intel video is having issues and nVidia works. Ubuntu won't be loading the same drivers, so whatever issue there is with the video card may only become exposed when running Windows drivers and features.

 

[ToastyKeycaps]

Could be an issue with the nVidia video card, does your external monitor show it's connected to the nVidia or the Intel video? Or Intel video is having issues and nVidia works. Ubuntu won't be loading the same drivers, so whatever issue there is with the video card may only become exposed when running Windows drivers and features.

Both GPUs work fine on both OSes. I don't think it has anything to do with drivers or GPUs. Also as I said, even BIOS and GRUB menu won't show up on the main screen, only external one. So the problem seems to be somewhere in BIOS(or UEFI whatever you call it). BIOS doesn't recognize the existence of the main screen and doesn't power it. The Windows and GRUB then agree with BIOS, while Ubuntu just doesn't care and uses main display regardless.

P. S. I tried to reset the BIOS settings and update it, it did not help.