Thanks for the update.
OK, we have 2 possibilities, MySQL is installed but not running, or it was not installed.
If you have followed step 12 as specified in the article, and did not see any errors, then it could be installed but not running.
In this case, run the following.
You should see something like.
mysql start/running, process xxxx
You can change/specify root password by issuing the following:
sudo dpkg-reconfigure mysql-server-5.5
The service would be stopped and you will be prompted to enter an new root password.
If you get an error, file not found, ..etc when running /etc/init.d/mysqld start then we have to assume that MySQL was not installed, or was removed.
In that case, do the following.
apt-get install postfix-mysql mysql-client mysql-server dovecot-mysql sudo
When asked to enter root password, choose and enter one.
Now you can use that root password when you install ISP Config.
If you see other issues, please post the output as you see it in your ssh window.