第30的语句：$pdo=new PDO(DSN,USER,PASS);

Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000] [1045] Access denied for user 'root'@'localhost' (using password: NO)' in C:\myphp_www\PHPTutorial\WWW\php\product\index.php:30 Stack trace: #0 C:\myphp_www\PHPTutorial\WWW\php\product\index.php(30): PDO->__construct('mysql:host=loca...', 'root', '') #1 {main} thrown in C:\myphp_www\PHPTutorial\WWW\php\product\index.php on line 30

请问这个问题怎么解决