Go to your database using phpmyadmin or whatever database utility you are most familiar with and look in the wa_settings table. See if you find two rows with a value for the "name" column of "adminusername" and "adminpassword" respectively.
If they don't exist, run this queries in the database:
INSERT INTO wa_settings (name, type, options, value, grp, subcategory, cond, description, variable, weight, spry_args, spry_error, help_text) VALUES ('admin_username', 'text', '', '[username]', 'Site Settings', null, null, '', 'Admin_Username', '72.00', ', \"none\", {isRequired:true, validateOn:[\"blur\", \"change\"]}', null, 'This is the Administrative Username that should be reserved for the website developer. Only this user will be able to modify the details of the Settings page. Additional administrative accounts can be created under the \'Users\' section of the PowerStore Admin - these users will not be able to modify these settings.');
INSERT INTO wa_settings (name, type, options, value, grp, subcategory, cond, description, variable, weight, spry_args, spry_error, help_text) VALUES ('admin_password', 'text', '', '[password]', 'Site Settings', null, null, '', 'Admin_Password', '73.00', null, null, null);
This will create the two entries and you can either update the [username] and [password] in the script before running it, or log in with those values and update it from the admin.