Assuming your database contains tables, try running the following:
$statement = $DBH->query('SHOW TABLES'); var_dump($statement->fetchAll(PDO::FETCH_COLUMN);
If the connection was successfully established, the example above should give you a list of available tables in the database you connected to.
As you noted in the comments, the
PDO object was created without any exceptions thrown. It just appears to you to be empty, that is probably all.