Call to a member function prepare() on a non-object

Почему мне показывает следующую ошибку, хотя запрос правильный?

Fatal error: Call to a member function prepare() on a non-object in X:\home\localhost\www\kbm\adm\functions.php on line 100

function get_orders($pdo) {
    $list = null;
    $style = null;
    $stmt = $pdo->prepare('SELECT * FROM orders'); //линия 100
    $stmt->execute();
    foreach ($stmt as $row) {
        if ($row['status'] == 'new') {
            $style = '';
        } else {
            $style = 'style="color: rgba(0,0,0,.2);text-shadow: none;"';
        }
        $list .= '<li><label '.$style.'><input type="radio" name="order" value="'.$row['id'].'">'.$row['id'].'. '.$row['userName'].' <sup><sub>'.date('d.m.y H:i', $row['timeOrder']).'</sub></sup></label></li>';
    }
    echo $list;
    $pdo = null;
}