First, you should not log in to the graphical environment as root. Could you log in as a normal user? Ubuntu doesn't support logging in as root.
Second, there is a good reason why the root account is disabled in Ubuntu. It is designed so that users that are members of the 'admin' group (e.g. the one user the installer creates) can gain root access with the
sudo command. While not recommended, you can enable the root account, and log in to a shell as root, but not to graphical environment. It is good practise to use
sudo when you need root access (or
gksudo for graphical applications). If you need a root shell to execute several commands as root, you can just open a shell with
sudo, for example:
sudo su -
But it is better to simply use
sudo for the command you need if you only want to execute a few commands.
Look here for more details: https://help.ubuntu.com/community/RootSudo