I've just joined today so I hope I can help youhere. I'm no IT techie but since Virgin Media took over NTL I have learned a lot!!! I had the same problems as you with a limited or no connectivity message. When the VM engineer called out he had to set my account up again on my Desktop PC and told me I would also have to register each of my laptops but wouldn't show me how. I found this on the internet so as long as youu have your PID and password you should be able to register. By the way, VM do charge 25p per min up to 10mins and then they have to call you back. They don't always so make sure you get a name. Good luck
Manual Auto-Registration procedure
In order to complete the registration of your cable modem or set top box, and to register for ntlworld username and ISP services, make sure that your PC is using your cable modem connection (not dial-up), then launch your web browser, which must have JavaScript enabled. If your web-browser hangs or gives an error page when launched, this might be because it is trying to connect to a home page which is disallowed until you have completed this registration: just click Stop. Send your web browser to
https://autoreg.autoregister.net/start.html (note the https rather than http) and follow the on-screen instructions. When asked for a Serial Number:
for stand-alone cable modem users, the serial number is ntl-ct8-cb485.
for digital TV set top box users, the serial number is ntl-ct8-cb487.