I know we had a lots of questions about that problem but none worked for me. I have a dual boot with Windows 10 and Ubuntu 14.04 but cannot change the brightness level just when I use Linux. The only way I've found to change it is using Nvidia Xserver application but I had read that this is not the properly way to do that. When I try to decrease the brightness level the bar on the top of the screen appears and tells me that it's decreasing but nothing happens. Please, help me.
Same issue here. Used this link and it works perfectly now. Although updating to the latest version of Ubuntu fixes it as well. http://itsfoss.com/fix-brightness-ubuntu-1310/