PROBLEM SOLVED !
Idk why it happens , but it may be any error : here's what I did :
I set the brightness in game settings BUT after that I haven't press "apply video" button that time . It turned out that without pressing this button all settings has been saved succesfully - I've just pressed the "back" button . The thing is that next time when I did the same but at the end I pressed "apply video" settings hasn't been saved ... that may be any bug ?
Has anyone had similar problems ?