According to Robin Walker's site, you generally have to use a straight-through cable to connect to a SACM - unless you have an ntl:home 100/120 (Ambit), in which case you can use straight-through or crossover.
http://homepage.ntlworld.com/robin.d.../ethernet.html
Zest - How long do you leave the modem off for before connecting it up & trying it again?