Sounds like a problem with your USRobotics modem.

If you can go in safe mode go in device manager, double click on the modem, click drivers on the top and choose Roll Back Driver and then reboot.

If that doesn't do it go back safe mode go in device manager, right click on the modem, choose uninstall and then reboot.

You can also try verifier.exe/create standard settings/automatically select all drivers.

If that doesn't do it remove the device from your PCI slot. There's a possibility of a hardware failure.