Cheers guys
I rang NTL CS - well I got someone to ring for me from a landline - they checked the modem at their end and said it was malfunctioning; no response etc. Which I was rather perplexed about as the connection, at least for the first few days, was never constantly dead, it was merely fluctual. Anyway, I arrange a technician to come around in a couple of days, put the phone down and come back to my PC and surprisingly the modem is back on and the internet is working again. I think I'll have the engineer come around regardless because after being told the modem was knackered, it's a tad strange.