before starting ISPconfig Installation ensure you are able to ping www.yourdomain.com
. you should get reply from your Static IP. if you get that everything is fine.
if you are not able to ping www.yourdomain.com
it's probably because your changes at the domain registrar's end like name server , A record are not updated.
you can also continue the installation using ispconfig server IP and later make the changes but for the changes to take effect it would take few hours.
if u have changed the name servers , A record it may take anywhere from 24 hours to 72 hours. normally it gets updated within 24 hours.
have a nice day