When moving your existing Joomla MySQL database to us, you need to create a new empty database and import your existing database into the new one. If you do not know how to do that, just follow the Transfer existing MySQL database FAQ. However, the new database has a different username, name and password and your Joomla configuration.php file still has the old ones.
Log into your cPanel -> File Manager and edit the following 3 lines in the configuration.php file.
If you find any difficulties, you can contact us in our 24/7 Live Chat, where a representative of ours will gladly help you out.