Spotlight occasionally fails to display the search dialogue when activate. This incorrect behaviour can easily be fixed.
Spotlight is activated by pressing Cmd-Spacebar or clicking the Spotlight icon on the menu bar. This brings up a search dialogue (or sheet, in Mac OS X lingo) where the keywords are entered. However, on occasions this dialogue is not displayed although the user input is recognised and processed.
The way to fix is is to delete or rename com.apple.systemuiserver.plist located under
Then, restart the computer.