error establishing a database connection

Hi, due to an infiltration into my Cpanel, I had Hostgator support change my username.

Now, when trying to log into my wordpress blog, i get the following message:

"Error establishing a database connection".

I edited the wp-config.php file changing old DB_NAME = old_db_name and DB_USER = old_db_user with new ones (DB_NAME = new_db_name, DB_USER = new_db_user), but still get the same error. What can i do to fix this isssue ?

Thanks in advance.