Sometimes, despite the best of intentions, it's hard to tell if 
the VNC server is running at all. Here are some ways to check
to see if it is:

1. On Windows, look for a VNC icon in the Taskbar tray. Position
   your mouse cursor over the icon, and it should report what IP
   address the VNC Server is running on.

2. On Windows, try running the "fport" utility. This will report
   all of the running servers and what port they are listening to.
   If you see VNC listening to port "590#" then you know it's
   accepting connections on VNC Viewer Display "#". So, if you see
   5905, then the Server is ready to handle "Display 5".

3. On Linux, check with lsof to see what's running (run as root):
   linux-box# lsof -i -n -P | grep -v 127.0.0.1
   See #2 above for what it means when you find something.

4. Lastly, try this: from another PC on the same LAN as the VNC
   server, open a telnet client and connect to the VNC ports:
   "telnet ip.address.of.server 5900". If you see a response which
   looks like "RFB 003.003" then the VNC Server is working.

Perhaps the easiest way to check if a VNC Server is running is
via the http://www.gotomyvnc.com service scan. Give it a try:
just open a web-browser on your VNC server and see if it works.