Suddenly, No Email!

A couple of days ago I was doing some work on my template for the home site in my wpmu installation. I was changing some html in the wp-signup.php file to work with my template. Now the thing doesn’t work. When I hit he “next” button it behaves as if I had hit the reload button, and no email is sent anywhere. I extracted the file from the archive I downloaded and put it in place, but that didn’t help. I’ve looked at all the mail server stuff, php settings, etc., but nothing seems to work!