[Rob]

You have your old PC and your new PC networked together, how? Is just one or both PCs connected directly to your modem / STB?

If it's both PCs connected directly, that will not work as the modem / STB can only see one PC at a time. When you disconnect one, you must power down the router and computer(s) before plugging in the other (only one at any one time), and then pwoering up.

To use both PCs at the same time, you must either have a router between the STB/modem and both PCs, or have only one PC directly connected to the modem / STB with the second PC connected by wire to the first using internet connection sharing.

As thread is a netorking issue, moved to Computers & IT