I have installed Tomcat 5.5 in my PC. When I connect my comp to the net and try working with tomcat, everything is fine. Unless I startup tomcat, I'm shown the error page when trying to access http://localhost:8080. Tomcat works fine and lets me run my apps.
However, when my computer is disconnected from the net, even though I can start tomcat, but I'm not able to access the http://localhost:8080 page. It neither takes me to the home page, nor does it show me an error. It just shows connecting.....and stays that way.
I may not be able to give you a solution but I also have somewhat similar issue with Sun's Glassfish server. I had installed it while connected to my work VPN and I can not access Glassfish console with http://localhost:port when I am not connected to VPN and I have to use the http://127.0.0.1:port (or IP assigned by the router, don't remember exactly). You may have installed Tomcat while connected to Internet and while Internet connection is ON the localhost is mapped to the IP assigned by your ISP and when you disconnect from Internet localhost may be getting mapped to Class C local address. Try looking at what IP is mapped to localhost when Internet is ON and when Internet is OFF.