Outlook Web Access

I’m trying to setup Outlook web Access (OWA) but keep getting the following message after I put in my logon details on the OWA screen ‘The Microsoft Exchange server is down or the HTTP service has been disabled by an administrator’. I have read through the articles related to this in technet, however these don’t seem to be much help. Also, the TCP/IP Port 80 is open on the firewall and I have tried to logon using a number of different accounts (including administrator). Can anyone help?