Hi My Mac Pro has no brightness control via the F1/F2 keys and yes I have the correct settings for function keys in prefs, and the USB cable is plugged in. Also the USB cable has been tried in all other ports, all resets have been tried to no avail. The ACD has been tested on another machine and works fine in every way, the keyboard has been tested on another machine and is also fine, so the problem lies within the Mac Pro in someway. This all started after I had to send back my ACD for repair and I had to use another display with my Mac Pro, then on return of my ACD the brightness controls refuse to work. The other thing is that the brightness slider in the Display Prefs has disappeared.