I've rebuilt my system and I can't get the PC (1394 net adapter) to connect to the router over cable. I can however connect over a wireless connection.

Any advice please

Are you sure you have all the drivers installed?

IEEE1394 is a firewire port. You can use it for networking but would need an adapter.

This is not the port you plug the RJ45 cable into, that would be your ethernet port. In that case, check your device manager for exclamation points. Most likely the driver for your on board ethernet or NIC is missing.