Can't connect to data base in using PHP in my website

Question

I can't connect to mysql database phpmyadmin I get following error.

SQLSTATE[HY000] [1045] Access denied for user 'root'@'localhost' (using password: NO)

My code is as follows:

try {
    $pdo = new PDO("mysql:host=$host;dbname=$dbname", $username, $password); 
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
    echo "Error: " . $e->getMessage();
}

I checked the database name, password, username, and priveledges .... nothing worked