My new macbook 2.5 just came in. I love this thing. It runs great. I just cannot figure out one thing. The brightness buttons don't seem to do anything. I press them and the graphic comes on the screen but the brightness doesn't change. The other function keys work fine. This happen on ac and on battery. Is there a setting I'm missing. If it matter I have the 94 screen. Which is from LG I think. Thanks for any help.