Well, give this a try (assuming the Ethernet connection is not working).
- Unplug the modem from the mains
- Plug the USB adapter into the PC.
- Let Windows find the new hardware. Put the CD in if Windows asks where to find the drivers. do NOT run the installer.
- Plug the modem into the mains.
- When the lights on the modem have settled down, plug the modem into the adapter.