I'm not sure how you managed to run nautilus, but either way:
- Open a nautilus window and press ctrl+l.
- Type in
/usr/share/applications
in the location bar, and press enter.
- Find the launcher for
ccsm
(Compiz Config Settings Manager).
- Run it by double clicking, and enable Unity from within the window again.
Unity should start again (if compiz is actually running). If it is not, then from here you have two options:
Either:
- Log out and log in again.
Or:
- Find the launcher for the terminal.
- Open the terminal and type in
unity & disown
(the whole line highlighted in grey including &).
- This should get you Unity again, and from here you should have no issues.