Hello.
When you try to register and click for the actual form, it simply redirects to a blank page where no form is to be found.
You can see it here: http://www.factoriadeautores.com
Empty page: No aplication form is to be found
When I clicked on your Login/Register link, it redirected me to your /wp-login.php page. Seems like you are using JetPack for your login form and not s2Member.
It´s true, but disabling the Jetpack login form, the page still appears blank.
I navigated my way to this page by clicking the “Register” (or whatever it says in the original language) link on wp-login.php: http://www.factoriadeautores.com/registro/
There is no login form on this page and when I viewed the source code I could find no form in the source code either. I do see that you are using a third-party plugin (User Access Manager) for logins, but there are no fields on the page related to registration or log in nor any “submit” actions related to registration or log in. If you’ve used an s2Member shortcode on this page, it is being totally ignored. This is most likely due to a theme or plugin conflict.
Jedi Shark is correct.
If you have s2member Pro and you set up a Stripe account you can use the built in registration form. That is what I did and it auto filled it in for me. I didn’t really have to do much there and have tested it and it works great.
I did not find anywhere on your site where I could set up a new account.
If I were you I would move the log-in directory to something other than the default. I used the WPS Hide Login plug-in myself to move it to another location. It disables your wp-login.php from outside viewers and then if only you log in with admin rights will it re-enable it for that user or users.
Doing that will prevent hackers and bots from trying to access your site.
I hope the Stripe option can work for you.