Geoff, if you want to get access via the web (using your browser), you should take a look at this tutorial here: https://www.nomachine.com/getting-started-with-web-based-access.
Port 4000 is for a native connection (i.e. when connecting from the traditional GUI, coming very soon for iPad). When connecting via browser to your remote machine, you need to check you have two things done: 1) have Cloud Server installed, and 2) port 4443 is set. This is explained more in the document above.