I'm now using Ubuntu 14.04.3 and using Unity tool for change some effects. Curiously, I changed Window spread to "on" in the Window spread tag, the system automatically logged out. When I tried to login, I entered the main screens but immediately the system logged out again. After efforts login few times, the situation still happened.
However, I login successfully with a Guest account. I tried some solutions on the Internet but there is no point to solve my problem. What should I do?