Go to My Computer > Properties > Device Manager > Network Adapters then remove the the device (obviously, not the hardware)... restart the windows. It is very obvious that the modem would still be in the Control Panel unless of course you will remove its driver using the Add/Remove Program in Control Panel...
Shutdown the computer, then remove the hardware device... Turn on the computer without the network device... That's it!
But wait, if you want to use the network device, then again... insert the network device in the slot alloted for the hardware... if this time the Windows did not detect your modem, there is a great chance and possibility that your modem is already defective or you hadn't inserted the modem very well.... If the windows detect the modem... then locate the driver that you had...
Why make things so much complicated?