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If you do have an ethernet port on your PC, it is worth trying it. As the network card has specific hardware on board, it can be more reliable and use less porcessor resources than the USB connection.
If you need to persist with USB, try experimenting by uninstalling the ntl USB drivers and installation, and in control panel, uninstall any networking connections. Reboot the PC, with wires unconnected, and allow it to reload only what it needs. Then simply copy the USB drivers from the NTL disk to the hard drive, don't install the disk as a whole.
This article may be of assistance:
http://www.cableforum.co.uk/board/article.php?a=13