1a) Please check that the domain is in none of the recycle bin's. If you find it there, empty the recycle bin.
1b) ISPConfig uses namebased vhosts. You must use the domain to connect to the vhost, not the IP. This means your domain must point with an A-Record to your server. If you server is behind a router, you must use your internal IP address for the website, not the erxternal IP.