First off, try refreshing your browser's cache. Your web browser may have hidden the options itself.
Then, maybe just replace your templates/subSilver/overall_header.tpl with the default one (or whichever style you're using).
Also, is the form still disabled when you go to http://www.yourforum.com/phpBB2/profile ... e=register
? If that form is working, then it should be one of the two problems above; if that form doesn't work, something else weird is going on.
The purpose of the admin panel switch was so that if you wanted to re-enable registrations, you wouldn't have to uninstall the MOD, but it should still be working. 8)