Under Ubuntu the access to root account is only blocked and only the sudo/gksu commands allow the use of features as superuser.
To enable the root account and access directly via the console in root mode, you must type the command:
$ sudo passwd root
This command allows you to set up the password modefor the root user which will be activate for the console sessions only (no GUI). Once the password is initialized, it will be possible to open a console session with the user root.
To enable access to the graphical user root, go to System/Administration/Login, click the Security tab, then tick the box allow connection of the local System Administrator.
Disconnect and reconnect with the root account.