With a registration page you wouldn't want them not to be able to register? Just prevent them from going to private pages by adding something like the following to those pages.
// First execute a common code to connect to the database and start the session
// At the top of the page check to see whether the user is logged in or not
// If they are not, redirect them to the login page.
// Remember that this die statement is absolutely critical. Without it,
// people can view your members-only content without logging in.
die("Redirecting to login.php");