I have a Dell as well with this issue and it is Ubuntu Specific. Fedora works and so does openSuse. It seems to be related to gnome-power- manager because if I close this process I can change my brightness.
-- Losing keyboard and mouse control when changing screen brightness with fn + arrow under intrepid https://bugs.launchpad.net/bugs/285323 You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gnome-power-manager in ubuntu. -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs