|If this device was provided by your ISP you'll have to contact their support people for help on it. At least, that's what I would do.|
From the sounds of it, this is a modem issue. If you want to be sure and you have another network ready computer or laptop handy you could connect them NIC to NIC with a crossover cable. Give them basic TCP/IP settings as follows:
Subnet Mask: 255.255.255.0
and they should be able to communicate. If they can, it's not your PC. If you have a switch or even a 4 LAN port router, you could connect two computers to the switch or router's LAN ports using regular network cables and accomplish the same thing. The special crossover cable is only required if you go directly from PC to PC (this includes laptops too).
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.