Have you allocated fixed IPs to devices? Do they correspond to the range the Hub works with?
As others say ... reboot everything. Start with a PC wired to the hub and work out from there.
Thanks for your help everyone. I rebooted all the equipment and they are now recognised by the HomeHub5.
Downside is that the BT Desktop help that I was advised to install has taken over the PC. Constant checking, popups with pointless advice and the hard disk seems to be thrashing away for no good reason.
Once I find out the address of the router to access it directly, I will bin the BT desktop help.
The next job is to find out who was accessing the Netgear router over the last three days. It was uploading and downloading huge amounts and I was hardly using it. The lights were flashing away all the time.
I changed the password and the Wi-Fi password but it still carried on. I even reset the router and gave it another name but it had no effect.
I think someone somehow had cloned it. Got the pin number.
When I removed the Netgear router, (Named Netgear40) and installed the BT router, I could still connect to a Netgear40 router.
So it is somewhere nearby. Possibly a couple of local teenagers.
I had thought that it was BT testing the line prior to setting up the Infinity2, but obviously not.