Using the the F3-key should normally activate Exposè/Mission Control. In some circumstances nothing happens when you hit the F3-key or the four finger up gesture.
To solve this problem apply the following defaults write command:
Mission Control
Disable automatically rearrange Spaces based on recent use
Mission Control gives you access to all your open windows and desktops (spaces). The spaces are automatically sorted by recent use, you can undo this.Use the following command in Terminal to change this.
Disable the Mission Control zoom effect in Mac OS X
Turn off Mission Control’s zoom effect that appear whenever it’s activated or deactivated in OS X 10.7 and above.
Mac OS X: Disable Mission Control and Spaces
If you never use Mission Control than it is possible to disable the feature entirely and save resources. If you disable Mission Control you also disable the Spaces feature, before disabling Mission Control, close all of your spaces.
Mission Control: Fullsize window previews
In OS X Lion the thumbnail previews of windows from the same app are grouped together. By hovering the mouse over these thumbnails and scrolling up, you can expand the group of windows. It is possible to display these windows in full size.
Enable the full size window preview in Mission Control
Mission Control groups previews of windows from the same app. By hovering the cursor over a these group and scrolling up, you can see that the group showing more detail in those behind the main window. With the following command you enable to see a full size preview of the contents.
Enable the hidden ‘go to recent space’ gesture
When you use Mission Control often, you’ll like the following defaults-write. It lets you immediately jump back to the most recently used Space. You can activate this option with a four-fingered double tap on the trackpad (or Magic Mouse). Enable the gesture with the following command: