Changed root password on my server, now can't login anymore

I decided to change the root password that came preset on a fresh DigitalOcean server (ubuntu 12.04).

I used the first answer to this post: How to change root password in ubuntu?

which is:

sudo -i
passwd

(set my new password on prompt)

sudo passwd -dl root

Now I can't login as root on tty1 on my server, nor can I access my server on Filezilla, etc...

What did I do wrong, and more importantly how can I recover my root login?

Thank you for your help.

The command

 sudo passwd -dl root

is for disabling root and removing root password. As explained in man passwd:

-d --delete

Delete a user's password (make it empty). This is a quick way to disable a password for an account. It will set the named account passwordless.

-l --lock

Lock the password of the named account. This option disables a
password by changing it to a value which matches no possible encrypted value (it adds a ´!´ at the beginning of the password).

So you just need to set root password again.

So, first execute in a terminal

sudo passwd root

or

sudo -i
passwd

you will be prompted for a new Unix password. Write it twice (second time for confirmation).

Then execute

sudo passwd -u root

to unlock the account. This should return

passwd: password expiry information changed

Now you will be able to access root. But it is not a good idea as you can see here.