Macbook Air does not work F1\F2\F3, what should I do?

Question

macOS

Hello everyone! I want to find solutions to a recent issue. Last night, sitting at my macbook air, I discovered that when I press the buttons for adjusting the brightness of the screen / keyboard / sound, and other function keys on my poppy, it stupidly does not respond. Checked in the virtual keyboard - the system understands what I'm pressing. Pressing F11 scatters all active windows to the sides of the screen - like a four-finger trackpad gesture.
In the mood
Please tell me what could be and where to look for the problem?
Macbook early 2015, OS X El Capitan if it matters.
PS in the keyboard settings, the checkbox "use F1 [...] as standard keys" is unchecked and has never been used

Answer 1

Fn + f1 key combination, and without Fn, only brightness will work on f1

Answer 2

Uncheck or use in conjunction with fn.