F12 key function is different

Hi,
There's gotta be a simple fix to this but I can't seem to stumble onto it.

My F12 key brings up/hides the Dashboard. Before I sent my MacBook in for repair during which my hard drive was wiped, my F12 key would spread out and display all my active windows on the desktop, a feature that I really liked. I was able to go to keyboard functions in Preferences and uncheck the box that assigned the Dashboard to the F12 key but now, of course, the F12 does nothing. So how do I get the F12 key to do what it did before?
Thanks in advance for any assistance!

System Preferences > Expose & Spaces (if you're not using Lion) or Mission Control (if you're using Lion). You can change your keybinding here. If you're using Lion, assign F12 to Mission Control and Expose if you're using something other than Lion.

Thanks

Thank you, Mr. Smith, for the very quick and accurate assistance. It is very much appreciated!