internal sever error when installing multisite!

the site in question is http://focuseyecenter.com/

This is a bit of an emergency, as I did not think I would get an internal server error by following the official guide.

I’m fairly new to both wordpress and FTP clients, however I decided to take a shot at installing multisite regardless.

I followed the wordpress multisite installation guide to a tee, or so I thought, and made the necessary additions to the .htaccess and wp-config.php files. however, when I transferred the files, I got an internal sever error. out of panic I restored the original files yet the error persists. What can I do to at least bring the site back to its orginal state?