If you experience issues where your client is not showing up on your MOM console and you have configured MOM correctly, look for event ID 26009
within your application event log on the client machine.
Its highly likely that you have not opened port 1270 on your firewall.

Open port 1270 and another event ID should appear. Event ID 26021 – The agent has restored communication to MOMservername.

Also, check that your registry settings are correct – see https://cloudbuild.co.uk/?p=1609

And the correct firewall ports are open – see https://cloudbuild.co.uk/?p=1630