Attempting to access the server via http://serverip:5000 (first tenant install). We only have one tenant on this box, so I can't try any different ports. Using Windows 2008 Server running IIS 7. The 3CX windows management console works fine locally.
For first tenant port is 5000 for second 6000 and so on. Can you see the first page where you enter your credentials or you see this page from the beginning? Are you accessing your server from local machine or from another machine? If its localhost try accessing from another machine. My opinion is that is something wrong with your IIS. If it doesn't work try to reinstall it.