Styles gone after editing config file

[aself]

I'm trying to edit my config files after changing nameservers. When I changed from

 define('HTTP_SERVER', 'http://myusername.hostname.com');
 define('HTTPS_SERVER', 'http://myusername.hostname.com');

to

 define('HTTP_SERVER', 'http://www.mydomain.com');
 define('HTTPS_SERVER', 'http://www.mydomain.com');

I lose my styles. Also, the links within the unstyled page return 404 errors.

I also cannot access my admin login page.

Thanks for any help!