Editing Config files properly plays important role in configuring database check your

define(‘DB_DRIVER’, ‘mysql’);
define(‘DB_HOSTNAME’, ‘localhost’);
define(‘DB_USERNAME’, ‘stoychev_test’);
define(‘DB_PASSWORD’, ‘123456789);
define(‘DB_DATABASE’, ‘stoychev_oc1551’);
define(‘DB_PREFIX’, ‘oc_’);

Please fill in your USERNAME, PASSWORD and DATABASE under the ‘DB_USERNAME’, ‘DB_PASSWORD’ and “DB_DATABASE’