Comment 2 for bug 1389888

I'm going to hazard a guess here.

The attached logs show a failure to load the nVidia 331.89 drivers because they don't support the hardware. You say you installed the nvidia-343 driver package from xorg-edgers, and I assume you followed that by rebooting so the kernel would pick up the new driver module and X would restart with its matching X driver.

What can sometimes happen with the Compiz window manager is that once the OpenGL plugin (required to run Unity) fails to load once, it seems to want to blacklist itself and never run again even after the initial cause has been addressed. If this is the case here, I suggest resetting the Compiz plugin configurations back to their original values by typing the following command at a command prompt.

  dconf reset -f /org/compiz/

Please try this and let us know if it works for you.