question about function keys on laptop

When I bought my MacBook a month ago I noticed that there was something I'd got *very* used to doing on my old iBook that I couldn't do anymore: pressing the f11 key to get all the windows to disappear and reveal the desktop. I was told that to do this I'd now have to press the fn key *as well* as the f11 key. This was a bit annoying but just when I was finally getting used to it, that method stopped working. Yesterday I was getting a thunk when I pressed this key combination but now I don't even get that. Nothing whatsoever happens. (When I press the f11 key without the fn key the sound level is increased, as is supposed to happen.)
I'm posting this in the hopes of avoiding having to take my computer back to the Apple store. Is there any chance that this is software problem that I could set right on my own? Any comments or advice would be much appreciated.

regards to all from flunn

Go to System Preferences> Expose and Spaces> Expose and check that the shortcuts are still set to F9-F12.

thanks to skaheadpunk

Thanks very much, skaheadpunk, for your reply. The problem is solved. (I'd never used exposé/spaces before—but obviously I changed the original settings in some way or another.)

regards to all from flunn

Also, if our keyboards are the same, my f3 key has a bunch of little boxes on it. That will give you a preview on screen of all your open windows. Not the same as the f11, but good to know.

How old is your Macbook? On the newer MBP's at least Expose got moved to F3 (it has an icon on the key that is a box with little boxes inside it). F11 and F12 were changed into volume control keys.