Refer to the following to set root login:

sudo -s (to become root)

vi /root/.ssh/authorized_keys

Delete the lines at the begining of the file until you get to the words ssh-rsa.

vi /etc/ssh/sshd_config

Set the variable PermitRootLogin to PermitRootLogin without-password (without quotes)

sudo /etc/init.d/sshd restar