Stage 1 here. You say you have only recently had ntl broadband installed. I suspect you are still posting htis using your DSL conection?
Can you confirm that you do actually have an internet connection via the Set Top Box (STB), or Cable Modem? Simply put, if you switch off the power to the modem / STB, unplu all ethernet (networking) cables from it to any computer or router, plug a single ethernet cable in between the Modem / STB and a computer, now power on the STB / router and then the connected computer, what happens?
Remember that every time you swap cabels around that plug in to computers / routers that the other end is plugged into the Modem / STB, the modem / STB must be powered off and then on again. It won't detect the change made otherwise?
edit: Aragorn spotted the big problem - no cable compatible router