I have a Sony Vaio laptop, and though I rarely need to use them, I find that holding the blue Fn button and pressing the "brightness +" button (F6) doesnt have any effect on the screen. Sometimes I need to brighten it a litle bit on sunny days (rare things) like today!
In general to find out how to brighten the screen is a very long winded process in Help! Remember the good old days when we had a brightness and contrast button, no menus, just turn it!!!!