You can run the following script for login to root without password -
You need to add your key to the root authorized_keys file on the server.
On the Server
sudo su - root
ssh-keygen (to make sure root has the .ssh directory etc)
Add your public key to .ssh/authorized_keys
Check your sshd_config settings (/etc/ssh/sshd_config) are correct one last time.
Ensure those settings take effect by restarting ssh: service ssh restart
On the Client
Login to the server as root using: ssh root@yourserveraddress
Note: If this doesn't work you'll need to do some further investigations.. Try posting the results of an ssh -v root@yourserveraddress.
Hope this will help you.