Network Adapter Problem

I just got a new cable modem that besides having an
ethernet connection has a USB connection. I used the USB
port and then tried to set up a network to my other
computer. Of course because the ethernet was not
connected this would not work. I then removed the USB
connection and plugged in my ethernet but the computer
now keeps saying that my network cable is unplugged. This
is not the case. I have called my ISP and they cannot
figure it out. They say I need a new network card.

Has anyone run into a similiar problem and if so how did
you fix it.

Thanks