Don't know if this might be any help. Scroll down to the paragraph headed 'Cable Modem registration guide' and look also at the following 'Important notice'
http://ecompany.ae/eco/isp/english/s...e/dpc2100.html
It may not apply to NTL versions, but then again you've tried just about everything else.
If that turns out not to be relevant the next thing I would do is start from basics. Boot to safe mode and remove all references to network card in Device Manager. Let windows re-discover it on reboot and re-install drivers. Then make sure you are set up to get IP and DNS automatically.