VNC FAQ-o-Matic : Troubleshooting Guides : Can you “ping” the VNC Server from the Viewer machine?
Since VNC connections travel over the same IP networks that any other sort of Internet connection does, it’s a good idea to verify that the network connection between you Viewer and Server is working. That’s what the “ping” command is good for. In Windows, open up a DOS Command line and type: ping [ip.adddress.of.Server] (eg, “ping 192.168.0.10”) …and see if it works correctly. If you can’t get a ping connection to work, it’s unlikely that you’ll be able to get a VNC connection to work.