Dash appears to run but is not visible

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http://askubuntu.com – I've an issue in an Ubuntu install that was upgraded to 12.04. Recently the Unity Launcher is behaving strangely: left-clicking the dash icon changes the title bar and a triangle appears next to it, suggesting that it is running but nothing else can be seen, It does not respond to keyboard input either. Using the "Super" key produces the same result (or lack of thereof). Right clicking on the dash icon only shows "Dash home" and it has the same non-effect as above. The red line is something new that wasn't there when the "Dash home" button worked correctly (yes this worked after the initial u (HowTos)