Error establishing a database connection…?

Hello guys, I’m trying to undertake the ridiculous change from wordpress.com to www.remarpro.com. Set up hosting and domain with hostgator and followed an online tutorial as i’m totally new to this. Changed my nameserver at Hostgator to what was emailed to me and now get this when I try and access my cpanel…

Error establishing a database connection

This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at localhost. This could mean your host’s database server is down.

Are you sure you have the correct username and password?
Are you sure that you have typed the correct hostname?
Are you sure that the database server is running?

If you’re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.

Have had nothing but problems… wish i’d just left it.

Cheers for any help,
Scott