login - After upgrade ubuntu 18.04 changed from GUI to Terminal

After upgrading from Ubuntu 17.10 to 18.04 I am not able to login to the desktop environment. This screen shows after restarting:

Your OS is not properly installed. Try the following:

exec sudo -i
dpkg --configure -a
apt-get -f install
apt-get update
apt-get dist-upgrade
apt-get install --reinstall ubuntu-desktop
apt-get autoremove
apt-get clean

If it doesn't work, reinstall Ubuntu.
Follow this to reinstall the OS without loosing data. The post is about Ubuntu 16.04 LTS but it'll also work for Ubuntu 18.04 LTS.