Hi Guys,
I want to add a register/login form on my wordpress website . Is there any free plugin that can do that ?
Thx in advance.

Theme My Login. And there's plugins like WP FB Autoconnect that will put a "Connect with Facebook" button next to the form and let people register that way.

I used to use Theme My Login, but recently that plugin caused some problem for my site. So had to take off.

There are many form plugins now that you can integrate with your Wordpress theme. Just install the necessary plugin and it should reconfigure and start working seamlessly.