我已经写在下面了 php 连接mysql数据库的代码：

<?php
// Connect to MySQL
$servername = "localhost";
$username = "user";
$password = "A11b22c33&";

// Create connection
$conn = new mysqli($servername, $username, $password);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";
?>

但是，此代码无法建立任何连接。我只得到以下错误：

currently unable to handle this request.
HTTP ERROR 500

但是，如果我删除了代码的连接部分 php 文件工作正常，即我收到的回音为“连接成功”

<?php
// Connect to MySQL
$servername = "localhost";
$username = "user";
$password = "A11b22c33&";

echo "Connected successfully";
?>

有人能帮我理解出了什么问题吗？我已经检查了用户名和密码，他们是完美的