joomla site login/sign up issue

[login to view URL] My joomla site was spammed with fake users so I deleted all the spammed users except for the original and real users (only around 20). Now I can't login using the original user's username and password, it takes me to a blank page whe I login. Likewise, singing up is an issue now. I will also need a recaptcha element in the sign up form to reduce future spamming.