登录表单允许使用空白用户名和密码进行访问

I'm trying to implement a PHP login script which works with 3 PHP files. The scripts work fine when using correct user names and passwords, and the script even blocks access when the wrong information is provided. My problem is that the script is allowing access when you press the submit button on the form and don't insert a user name or password. I'm trying to implement a PHP login script whic