Just got a new 17" PB (It's wonderful!), but this is my 1st Mac in over 10 years. (Still have my LCII). I can't seem to get Expose to work. If I press F9 or F10, I get a shadow error window of some kind with the symbol that's on those keys, with a circle/slash and nothing happens. If I hit F11, the windows clear to the desktop like they're supposed to, but the 9 and 10 keys don't do anything. What am I doing wrong?