Same issue, same hosting company.....
I am having the same problem. I did get thru to adding the serial number so it reached the database.php file and that's where I received the same message "Safari can't open the page "http://www.yourdomain.com/install_cms/database.php" because the server unexpectedly dropped the connection. This sometimes occurs when the server is busy. Wait for a few minutes, and then try again. "
I checked my PowerCMS activations and it showed the domain i was attempting to install on but no other domains, but, it never got any further than the database.php file during the installation. In Chrome is said "No data received ERR_EMPTY_RESPONSE"