Right, so this is the CMS login page.
When you ran the install script to install Power CMS, it would have asked you to set a Super Admin username and password.
if you do not remember the super admin user and password that you entered, you can find it in the power CMS database.
USe PHPMyAdmin or another MySQL GUI tool to access the site database and look in the wa_settings table, the super admin username and password are stored in that table.