The code that you have here looks like it should be selecting the record for the user where the id matches the $_GET['user_id'] value. This is not very secure though as a user could edit the id to be whatever they would like.
Also, when your form post this value will no longer be present, you have the form set like this:
<form id="frm_login" name="frm_login" method="POST">
So your get value will not exist once the form has been posted. The better way to do this is to query the user table based on the entered email address, then send the users details to that address they entered. This way a users details will only be sent to the email address on file for that user.