Reloads the page?? Clicking on the register button should take you the standard wp register page. What is the URL of the button? And link to site? And remember, registering and logging in is a wp function.

Are you using a registration or some kind of membership plugin?
The ‘Register’ button in the forum itself should be a direct link to the WordPress register page. Is that what you are clicking when trying to register or something else?

Have a link to your forum so we could look at it?