The original posting sounds a carbon copy of my own experience at the moment.
--- on the phone with various people at NTL, and i've tried everything they've suggested, to no avail. The weird thing is that the pc is recognising the connection, as I get to the authentication stage, and I get a valid IP address when i cmd *ipconfig*.
The problem seems to be that i can't access the secure authentication site that they told me to try, 80.5.178.26 - it gives me the secure site warning but then doesn't load the page.----
I have a:
New NTL :250 Cable box replacing an NTL Pace STB
No router, ethernet connection, no firewall, checked numerous .dlls
Cleared History, Cookies and temp files.
Put
https://autoreg.autoregister.net into trusted site
I can ping 62.253.162.30 but not 80.5.178.26
I have spoken to NTL on 17 Sept and 19 Sept and spent some time last night checking everything again - Modem lights, connections, absence of firewall, etc

Well what's next?? Is it possible for the NTL crew to manually assign the MAC address??
I must admit that I am already thinking of trying a different supplier even though NTL offer a good product. ADSL doesn't appeal.