Comment 38 for bug 1285444

Using 16.04 had the same problem with blank screen. The first thing I tried was running 'unity-tweak-tool --reset-unity' but that made it even worse: before the windows had borders & top bar and I could use some shortcuts such as ctrl-alt-T to pull up gnome-terminal (but not custom shortcuts) and alt-tab to switch screens but that was lost after that command.

Removing ~/.config/dconf/user made it work again as noted above, but specifically something in /org/compiz since running 'dconf reset -f /org/compiz/' worked too.

I then reverted back to the problematic file and tried resetting /org/compiz/profiles/unity and the only thing that fixed was the alt-tab, shortcuts and window borders again. So there seems to be another bug since shortcuts are located in org/gnome/settings-daemon/plugins/media-keys

Running 'gnome-session-quit --force' gets an error which normally doesn't happen when it's working normally:
** (gnome-session-quit:3002): WARNING **: Failed to call logout: GDBus.Error:org.gnome.SessionManager.NotInRunning: Logout interface is only available during the Running phase

Attached is a dconf dump of /org/compiz