Today I booted to my Ubuntu but it welcomed me with a blank screen without any light from the screen.
I thought it is the normal brightness and back-light problem so I tried to turn up brightness level from keyboard but nothing happened.
Then when I tried to adjust volume using keyboard, I was surprised(or rather not surprised) to hear the usual sound effect from Ubuntu system. So I was assured that the system has been booted properly and the only problem is that the screen did not show up.
Intuitively, I thought of the possibility that the screen is actually “turned off” the same way as the brightness was set to zero on boot. With that I tried to press the keyboard combination to “turn on” the screen, which is “Fn+F2” (for my Lenovo Y410P).
And yes, I got back my Ubuntu desktop. Pressing the keys again will give me blank screen again(as expected since it is indeed designed to work).
No idea why the screen was initially turned off though.