Hi,

Whilst developing a new script, I always find it helpful to have PHP error messages turned on. The setting for this can be found in the php.ini file on your server/computer.

Also, it might be worth printing to the screen your SQL query before you execute it and then to die the script.
echo $query;
die;

This will allow you to check the query is correct. And also, you can run it on the MySQL command line or in phpMyAdmin, etc to see if it does actually find a result.

Another obvious one to check, but I made this error before and it took me a while to figure it. Make sure you're hashing the password stored in the database. Once I had a plain text password stored and I was hashing the password for use in the SQL query and I was wondering why it wasn't working - duh!

Best,
R.