page /wp-signup.php not working.

hi, i have problem with register page.

this is my setting:

1. Network setting > "Logged in users may register new sites."

2. Create page 'REGISTER' on buddypress setting page.

- when i go to mydomain.com/register @ mydomain.com/wp-signup.php have no registration form there.. the page said "User registration is currently not allowed."

- when i set on network setting > "Both sites and user accounts can be registered." i can't access on my site, just a blank white page..

what should i do?