I have a HP Elitebook 8560w and I installed Ubuntu 12.04 on it. I can't adjust the screen brightness even though I can use the slider to lower the screen brightness, it doesn't have any effect. I searched a lot about this, but nothing seems to work. I edited the grub file, but it still doesn't work. I installed xbacklight, and if I use the command "xbacklight -20" the brightness still doesn't change. So is there even a way to fix this, because it seems I tried almost everything.