No database connection

Hi
I recently moved hosting for a site and have subsequently moved back as it didn’t work out – I left all files and databases intact and have just changed DNS settings back to the original but can’r access the site, getting this message:

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 213.175.211.90. 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.

My original databases are intact and I have made no changes to the site since moving. 213.175.211.90. is the IP address of the server I moved to and am no longer hosted on.
Any help greatly appreciated as I’m completely stumped
Nick Garnett