This happens to me sometimes and I locate the contact information for the website owner, moderator, or administrator. It should be an email address. Then I email them from my own emal box letting them know I are interested in registering but theres a problem in their registration area- that the security anti spam letters are not showing up on the screen for you to type them in. Then I wait. I usually get an email back with in a day or so telling me they thank me for notifying them of the problem and it is being fixed or worked on and when I should be able to register.

is there contact information somewhere on the site you are wanting to register for and if so try emailing them