OK I work at a school and they have old iBooks, only one of them will only TAB if you hold down the shift key. I've looked in the system preferences in keyboard/mouse and also the international settings to see if the nation has been changed but nothing has. I figure if the TAB key was BROKE it wouldn't work even when you press shift, so that leads me to think its a setting. It doesn't work by itself under any user, or in any application. I could be in Word or in safari or firefox and it still requires you to hold shift. Any suggestions?