Site is not loading css js ect…

Hello,
I have been using wordpress on my domain for about 2 year. When I first got my site set up I began the multisite process but never finished it. And now when I try to finish the set up, after I add the code to my /config.php and my .htaccess, I login again to find /wp-admin is gone and the site is in standard text. Please help. Is there a way to reset my previous multisite settings? I cannot do anything which will result in content loss. I already have a popular and highly visited site running and do not want to run the risk of losing anything.