Your template looks to be trying to apply very generic styles to all modals on the page. Specifically, the below style in your template.css file is the main culprit:
#jsn-master .modal {
position: static;
}
Remove that, and it will fix the popup. There are other styles which are affecting the inputs from there, but that should get you started. You may want to try the Default SCLogin style to see if that helps with the other issues.
I hope that helps,
Alex