ok, lets try & sort a few things out here..
if its a SACM ( modem ) then your never going to get to start.ntl in a million years...
pinging 127.0.0.1 wont prove much apart from the Nic is actually there...
Im guessing the Cm is picking up an ip something like 192.168.10/11...
so has been stated above its one of a few things, Co-ax unscrewed, check it just be sure, once more, just in case, make sure its tight...
are the Synch & rdy lights on the CM both solid, if not either network fault, or CM buggered, either way you wont be fixing it, you need to call Tech support ( 0845 650 0121 )
basically if the coax is screwed in properly, you havent got a network set up or specified the 192 ip, its pretty much going to be CM/Network side of things, so give tech support a ring again, & just say your picking up the 192ip off the Cm, they should ( Crosses fingers ) recognise this issue & book an engineer for you.....
Regards
Barfly