Did you create a new database name? It's lookslike for me that your database name is inncorrect. Please check this out in your DirectAdmin (or kind of other system) by your database what you want to work with your website. Use that DB User and put it in the line 24. For example:
/** MySQL database username */
define('DB_USER', ‘CHANGE HERE THE CORRECT USERNAME');
Update also your password in your database, and fill this in where you find your password in your wp-config file.
Warning!! Before your change something, please make a back-up of your website and database! I am not responsible for errors or demage.
Please check this out if it resolve your problem. I will help you if you still have problems.