错误：SQLSTATE [HY000] [2002]无法建立连接，因为目标计算机主动拒绝?mysql

我调试代码时突然发生错误。它具有与数据库连接有关的一系列错误。

ERROR: SQLSTATE[HY000] [2002] No connection could be made because the target machine actively refused it. ( ! ) Fatal error: Uncaught exception 'PDOException' with message ' in C:\wamp\www\web\main\users.php on line 15 ( ! ) PDOException: SQLSTATE[HY000] [2002] No connection could be made because the target machine actively refused it. in C:\wamp\www\web\main\users.php on line 15 这是错误所指向的代码

function __construct() { $this->con = new PDO("mysql:host=".$this->host.";dbname=".$this->db,$this->user,$this->pass); } 我不知道该怎么办，因为我通常不会遇到这样的问题，所以我对WAMP的研究并不多。感谢您的帮助。