You are talking about login on SSH. By default, Amazon AMI do not allow root to being logued, also force you to use key pairs. This a HOT question for all AMI users and the first think i modify when test long time ago.
Remove old ec2-user keys:`rm /home/ec2-user/.ssh/authorized_keys`
Now allow root login and login by password by editing file: /etc/ssh/sshd_config.
You have to search for that and set yes to both:
- PasswordAuthentication yes
- PermitRootLogin yes
Do not forget to:
`/etc/init.d/sshd restart` or `service sshd restart`
Also, set a default password for root using command: 'sudo passwd root`