It should've just been a case of turn off & on again.
Hmm.
As you use USB for the PC, it may be that the modem isn't releasing the IP properly, or perhaps even the ethernet port doesn't work?
Swapping from USB to ethernet should be the same as swapping devices:
http://homepage.ntlworld.com/robin.d...b.html#usbswap
Have a read of this:
http://www.cableforum.co.uk/board/15...onnection.html
Have you considered getting a router?