How do I install ISPCONFIG IN A VIRTUAL HOST?

[fedora777]

I tried to install Ispconfig. Everything went fine until I reach the part where it asked me the following:

please enter URL (www) --- I entered www
ok
Please enter domain (e.g. xyz.de) -- I entered the FQDN of our nameserver.

It gave me this response the URL is unreachable!

So I tried another FQDN which is in the same server. It went through. I chose, http after that by the way.

Then I tried accessing it, the server is telling me that the page is not found or server cannot connect.

How do you install ISPconfig in a virtual host? (Where a few domains already exist in the same server?)

Thanks.