If the person running the site is using a dynamic ip service like no-ip or dyn-dns then that could explain it. Open up a command promp and then type nslookup *sitename* and it should give you a numeric address.
Type that address into internet explorer IE
http://111.111.111.111
If you have to connect to a different port put the port number on the end IE
http://111.111.111.111:port number