NFA requires port 8381 and port 80 to be open between the remote client and the NFA Console when accessing it remotely.
When using https NFA requires ports 8382 and 443 to be open between the remote client and the NFA Console server.
1. Ensure that any external firewall is allowing traffic on these ports.
2. Ensure that Windows Firewall is either disabled or allowing these ports.
You can check Windows Firewall settings by going to:
Administrative Tools->Windows Firewall with Advanced Security and making sure it says that is is "Off" for for Domain Profile, Private Profile, and Public profile as in the screenshot below:
3. Once disabled try to access the NFA website again.