Wish I could tell you. Some of the cheaper ethernet cables don't actually have all 8 pins connected because the newer NICS don't need it. Before you go driving a few hundred miles could you rig up a small test system with a battery, a bulb and a couple of wires to test the continuity of each of the internal wires?
Trouble is that if both the old internal NIC and the new PCI one display the same error message I can't think of anything else that could be causing the problem.
One final thing we could try is to go into Device Manager, open Network Adaptors, right click on each one in turn and choose Uninstall. I would re-enable the original one in the BIOS before uninstalling so they are both visible. Then reboot the PC and let Windows reinstall them both. Then try the connection again.
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.