There should be no need to use proxy settings with a single PC, using IE and connected to NTL.
To check whether you have proxy settings enabled, open IE, click Tools > Internet Options > Connections > LAN settings. If it is ticked, untick the 'Use a proxy server...' box.
If you have a setup other than a single PC connected to a set-top box or cable modem, please describe your setup in more detail.
If you want to continue using proxy settings, and need advice on how to configure them correctly, click here
For general connection trouble-shooting, click here