By default there is no permission to login as ROOT in Ubuntu, because of the security reasons. But you can be able to reset those setting by editing the configuration files. So try the following tip to enable the ROOT User login. 
Here the gdm stands for Gnome Display Manager.
Shell Command for Ubuntu 8.04
sudo cp /etc/gdm/gdm.conf /etc/gdm/gdm.conf.bkp sudo gedit /etc/gdm/gdm.conf
If the terminal asked for the root password please provide that. After that you will get the conf file in gedit.
Search the “AllowRoot” keyword, and if you found something like “AllowRoot=false“ change it to “AllowRoot=true”. Save the file close the editor.
Restart the machine.
Note: In Ubuntu 9.10 there is no option to enable the root login. 
hello midhun,
its a new information,i searched many sites about this…thanks
Hi Midhun,
Very nice article