If your tablet and PC are on the same subnet it should work. You don't need to enter the port number unless you've changed the default port on your PC.

Have you ever connected to your PC running VNC from any other computer?

Is your tablet getting an IP address from the SMC? Confirm that you are on your wireless network by opening a browser window and see if you can reach the Internet. Connect to Google for example.

Check that the IP address being given to your tablet is in the same subnet as your PC. You might install WifiInfo on your tablet and to check the IP handed out to your tablet.