IIS 6.0 does not respond/disconnects immediate

Weird issue here and would appreciate any thoughts. Have a SBS 2003
server that's been working without a hitch for more than a year. IIS
is only used to provide OWA access for Exchange. Yesterday, access to
OWA was lost. However, I cannot find any signs of the problems,
except that IIS is not serving any web pages for any sites (ie.
Default web site, Sharepoint, Admin, etc..). Things I have tried:

1. Setup a simple test web site with a single HTML page. The site
cannot be accessed.
2. Restarted IIS and Exchange services several times. Still no
response.
3. Exchange is working fine (ie. can send/receive messages).
4. Firewall is disabled on the server.
5. Network access to the server is fine and can browse from the
server to external websites.
6. Checked IIS logs and Event viewers for any error messages.
Nothing found except entries in IIS logs stopped around 2:00am
yesterday.
7. If I telnet into the server on port 80, i get an immediate
disconnect, no response text whatsoever.
8. No new applications have been installed on the network or server
recently.

Any thoughts or ideas (other than the obvious, re-install IIS).
Thanks,

Alex