is the ip address either 192.168.100.10 or 192.168.100.3 ?
if so, it means that the pc is not leasing a public ip address from ntl's network for some reason... it could be an ip shortage in your area, or a problem with the cable modem, but either way you will need to get in contact with tech support.
If the ip address is anything else, post back with what it is, and what the default gateway is. If it starts 192 it is safe to post the full ip in public because it is a private address anyway
