Ubuntu :: Root User Directory Does Not Exist, Root Password Not Recognised?

I no longer have access to my root desktop. On a session I attempted to change the root username but i apparently assigned it a wrong directory that does not exist. When I rebooted with my new root username, i was instead recognised as a simple user (no root privileges). I tried the console to change to "old" root but root password is not accepted and there is no way to access to sudoer files. it seems that inserting a new username requires root privileges and i am back to square one. Simply logging with old root username and password after restart gives me a blank screen with nothing on it and cannot even reboot.