Unity 3D (the default desktop) is actually a plug-in that runs on top of the 3D graphics rendering manager called Compiz. And I honestly don’t know whether it’s Compiz, Unity or the GPU driver to be blamed here because since its introduction Unity has had a lot of issues (crashing, top panel disappearing all of a sudden etc).
Not just Unity actually, to be fair, the Gnome Shell which also uses a similar 3D rendering technology is known for its similar “issues” as well. I don’t know how it’s with you guys but the recently introduced 11.10 Oneiric has fixed a lot of these issues and as a result now it feels much more stable.
Nevertheless, there were few occasions where my Unity (both 3D and 2D) desktops just “lost” the top panel plus had issues not showing the Application launcher… which pretty much destroyed the functionality of desktop.
This trick may not work all the time but in most situations as long as you can open a Terminal window, you can try a command that should restart the Unity 2D/3D desktops and get it up and running.
So when you’re in trouble, just press “Ctrl” + “Alt” + “t” keys which to open a new Terminal window and enter the below command and press enter.
This should restart the Unity desktop but sometimes it may take few seconds to load everything. That’s about it!.
However this command is different from the “Unity --reset” one since that one actually replaces your custom Compiz settings/edits … so if you wanna try to recover Unity without changing those values then this is the that you should be using.
You can also learn few basic things about this command by reading its manual which you can access by using the command below.
So in times of darkness where there’s no visible “light”, perhaps this might rescue you ;-). Good luck. Oh BTW, use it at your own risk too :D.