Unity doesn't load any GUI with a Nvidia card

After a reboot, and not after doing anything that could justify this, my Ubuntu 13.04 system is completely dead, in that every time I boot, and after I log in, there's no launcher and no system bar on the top. The desktop looks fine, but there's no way to run any program.

Since the only icon I have on the desktop is, incidentally, an .odt document, I have tried to double click on it, and it opens in OpenOffice Write just fine, but the windows have no borders or title bar.

It looks like the most basic window manager is not running. I don't know whether it's Unity, or Compiz, or what.

The last things I had done before the last boot were:

• install virtualbox and create a virtual machine
• sudo apt-get install nvidia-current

So I have entered a virtual terminal and removed both virtualbox and nvidia-current (sudo apt-get remove...), but that hasn't fixed the issue.

My system is completely unusable. I have rebooted three times without luck. What can I do?

I tried:

1. ccsm -> try to enable the "Unity plugin". It has no checkbox (like the one depicted in the screenshots in other answers), so I click on it as if it was a button, and it leads to a screen where there is a checkbox that says "enable Unity plugin". That issues a warning that another plugin is required, it prompts whether to not enable Unity plugin or enable the other one that is required, I choose the latter, and so on for a couple more plugins. At the end, it is impossible to close the ccsm window, because the "close" button does nothing, and there is no window bar.

   This doesn't change a thing. Even after logging out/in (which I perform by killing xorg) or rebooting, I'm still stuck with an empty desktop with no unity launcher or top sytem bar.

2. dconf reset -f /org/compiz/ and unity --reset-icons & disown

   Outcome: it vomits dozens of compiz errors (can't init this and that plugin, fatal dunnowwhat, something() unavailable on screen 0, and a lot more) and ends with a segfault. Doesn't fix the issue.

3. deleted .config/compiz-1 folder tree in my home directory, with or without going to Ctrl + Alt + F1 Didn't change a thing

4. the farthest I've been able to go is the following, which does get me Unity running but without the nvidia drivers and with only 640x480 resolution:

   • sudo apt-get remove nvidia-304
   • reboot => now my screen is 640x480
   • dconf reset -f /org/compiz/ && setsid unity

   This brings up the loved and familiar Unity shell. However, if I go to System Settings and Display, the only available resolution is 640x480. I guess it is the one my non-nvidia card supports (though it seems pretty strange to me: I thought this computer had an Intel HD4000 GPU which should support pretty good resolutions)

5. after this, I tried reinstalling nvidia-current (which installs nvidia-304) and then I repeated dconf reset -f /org/compiz/ && setsid unity, but this has the same outcome as (2)

6. uninstalled nvidia-304 again, and tried with sudo apt-get install nvidia-310, and again reset -f /org/compiz/ && setsid unity Same outcome as (5) and (2).