Hlo.
I had the same problem as you. I tried Belkin, Linksys and Netgear routers(two of each cos they claimed that they must be 'faulty') with my then Telewest cable and powering everything up numerous times in the right order, cloning MAC addresses, you name it, it simply would not connect. I went through hours of tech support with Belkin and Linksys and they couldn't help in the end.
I phoned Telewest loads of times and they didn't help. In the end, I gave up trying to get wireless, there was nothing I could do. How come there are a lot of happy customers who use exactly the same service and the same gear and seemingly connect first time?
By the way, if anyone would like to help, I'm on Virgin cable now (as everyone) with Motorola surfboard modem and I have a Linksys laptop wireless card waiting and I'm open to any suggestions of a router that might WORK!