Cannot login in front or back end or register for Joomlasite

I was trying to install a sobi2 plugin, I changed permission in [login to view URL] to 777, and also in another file, and now I cant login in to the front end or backend of my joomla site. Also, no one can register. I dont know if this enabled a hack or what. I have had 2 freelancers look at it already and neither have been able to diagnose the problem. It is not a password issue...it is something much bigger. I cant imagine what is wrong, but I need it fixed as quickly as possible. I am looking for someone that can start right this second and stay in communication with me. Thanks.