How to disable Password Validation?

I'm using asp:login to build my login page. 
The thing is many of my user doesn't have a password,  only the admin and super user had password. 
I managed to stop the password validation, but the password text box keep required the user to enter password. 
Even, the entered password is not correct, the page will still direct the user to the main page. 
So, my question is :
1. How to stop the password text box from prompting the user to enter the password (even the password is incorrect)?


So, I try to build the login menu without the use of  asp:Login. But this time I have more question. This is the flow of the login screen:
1. When UserID is correct, then will check whether the user had a password or not.
2. If the user had password, then only the password text box will be shown.
So, my question is :
1. How to check from SQL Server that my user had pass ...