I am having a hard time understanding exactly what the problem is.
From what I understand:
You have a new modem that connects to your computer with a USB cable.
Your computer is not accepting the USB connected modem.
There is a light somewhere that keeps flashing on and off.
So lets start over...
You have the "Cable" Coax cable plugged into the back of the modem right?
You then connect the Modem to you machine with the USB cable right?
Did you get any software for the modem that you need to install on the machine?