(I'm not looking for any help with this, Just accepting my fate and moving on.)Today, I noticed my desktop was loading web pages very sluggish, so I did a speedtest; I only got a little over 1.74 Mb/s down, when I pay for 150+Mb/s down. So I looked at the task tray, and it's saying there's nothing connected to LAN, defaulting to my crappy Wi-Fi. But my Ethernet cable is (and has been) perfectly good. Rebooted the router, switched router ports, and I even recapped the cable with new caps on each end (it's 30 feet), but nothing helped. So I booted Linux Mint 18, and the problem persists... (It appears to load drivers fine and acts normal, but no cable connected.) So it's confirmed to be a hardware problem, not a Windows-specific issue. The router port's LED just flashes an orange light instead of green, and I get no LED activity on the PC side's LAN port at all.
I've taken to using my Wii U's USB-to-Ethernet adapter to bring my speeds back up into the 90Mb/s range for now, but it looks like I just need to spend like $10 on a PCI Gigabit Ethernet card.
Hoped you enjoyed the read.