how can I delete the below mentioned page?
http://www.columbusorg.com/register...login.aspx

Please let me know. Thanks

If this is a custom Login page that you created, you'll want to do two things:

1. Go to Admin, Site Settings, Advanced Settings and reset the Login Page to . This will result in the site using the default page.
2. Go to Admin, Page Management and delete your custom page.

Because Step 1 above effectively removes your custom page, you might keep the custom page if you decide to do something different.

And, because you are altering the login behavior, make a backup first.

How can I delete the registration form permanently ? Or is there any way to add captcha field on it?

Please let me know.

Thanks

You cannot delete the built in Registration page. You can create your own registration page and use that instead of the built in version.

What problem are you trying to solve by deleting the built in Registration page?

You can add Captcha. This is on the Site Settings page.

If you look at the other message in the forums that have to do with spam registrations, you'll find links to several approaches to dealing with spam registrations.