My laptop screen is black while my secondary screen is fine.

• What I tried:

  • setting brightness (Fn keys) - no effect, no change seen, also on secondary screen
  • removing static electricity like suggested here - no effect
  • restarting / charging battery, running on battery / "wall" power - no effect as well
  • wait to see if warming it up helps - it doesn't
  • follow official Ubuntu diagnostics - checking now...

• What I will try next:

  • check last updates I've made
  • IIRC I am running on nomodeset already, but can't recall how to verify this

Further symptoms:

• can't see BIOS screen
• system loads and works fine, just screen has problems
• screen works (occasionally I could glimpse very dimly what was going on, but it was like with minimum brightness set - nearly non-distinguishable from just a black screen)

Any ideas how to proceed best? What is most probable cause?