Noob!! help needed with VM modem please

[sbg123]

have now tried so many macs ive lost count, all have done the same, am i doing something wrong? all i was told to do was put in a mac, but still getting unidentified network after 40 seconds when i connect the coax!! also have only had vm services in this property installed about 12 months ago, are there new settings needed or have vm updated the docsis at this period to prevent this working?