iMac display -- can't change screen brightness on bootcamp with Windows 7 I can't change iMac (2011) display brightness on bootcamp with Windows 7. When I press F1 it shows icon and even fill the bar, but nothing happen to display.

What have I tried:


Reinstalling support files
Installing fresh drivers from ATI site.
Changing screen brigtness in windows "Power Options".
I solved my problem, but I don't actually know what solved it:


I rebooted manualy without any third-party software like BootChamp.
I was pressing Alt (option) key when booted.