Recently the brightness controls disappeared from my Windows 7 installation and I had absolutely no idea why. I reinstalled nvidia and intel drivers (I have optimus) and it still didn’t work. Finally, after searching around, I found this post which said that the problem appeared to be because of TeamViewer. I uninstalled it and voila! The fn+Right and Fn+Left keys are working again. Thank goodness, it was getting a bit too painful.