The driver is definitely where I would start as well as the Ethernet cable.
Also, re-boot your router.
Sorry, but I'm not familiar with the "auto-MDIX feature" of Ethernet. Can you tell me more about it, please?
Even if you have the most recent Ethernet driver version, I would suggest that you get a fresh driver and install it. It can't hurt at this point.
What Ethernet do you have and do you know the driver name? Check Device Manager, please.