I suggest to copy all settings (port forwarding e t.c.) and disable firewall. If that won't help - please create a tech support ticket on our website.

If you had port forwarding settings at old router, you need to copy them to a new one.

Your computers are in an internal network behind a NAT based router.
Only the router has a public IP address. You can access your internal
network computers via the Internet. To do this you need to configure
'Forwarding' on the router/firewall. Configure the router to forward
connections from a port on the router to a specific IP address and
port (Radmin server's default port is 4899) of the target computer in
your internal network. You need to assign a port on the router for
every computer you need to access. The router will then forward the
connection to your computer in the internal network.

For instance, one of my pcs is on 192.168.1.68.

When I enter that into the Radmin Viewer on another pc, it refuses to connect.

All this was setup before, but now, since changing to the new BT homehub router, it will not connect.