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。