I'm having a major issue with my 2mb NTL broadband (connected through samsung set top box) basically, I was disconnected (wrongly NTL

) from my services and when I was reconnected everything came up aside from the broadband, after several calls to customer service, I was eventually put through to tech support, who advised me to reset my TCP/IP, winsock, etc.
When this still failed to resolve my issues, an engineer was sent out, who plugged my ethernet cable straight into his laptop and low and behold the broadband worked perfectly, this was despite me trying it on both my PCs, which have both previously had no issues with the broadband.
After calling tech Support again, I was advised to "take computer to computer shop and reinstall TCP/IP"
However TCP/IP is a core component of Windows XP and I can't do that, resetting the registry using the netshell command has not solved my issue, I'm still getting "limited or no connectivity" on both my PCs.
It's driving me mad! Can someone please suggest a solution?
Thanks!