Database Connection Error

I downloaded WordPress. Then I went online and created a subdomain (blog.mysite.com). I then went into mysite.com and created a database with a username and password. It gave me the option of “generate password,” so I clicked it and apparently got a second password. I left host set at the default, “localhost.” (I’m using C-Panel.)

I then renamed the sample config file to wp-config.php and published it online. When I visit blog.mysite.com/wordpress/wp-admin/setup-config.php I get this message:

“The file ‘wp-config.php’ already exists. If you need to reset any of the configuration items in this file, please delete it first. You may try installing now.”

When I click “installing now,” I get this error message:

Error establishing a database connection

But it doesn’t tell me what the error is. I’ve tried it with both passwords, and I’ve changed “localhost” to “localhost:3306” and “3306” (based on server: localhost:3306).

So how am I supposed to figure out what the database problem is?