I reconnected my computer yesterday after moving into a new home. Last night I couldn't get online so I decided to check my connections. My ethernet cable, where it plugged in to my Versalink 7500 Gateway, was extremely hot. The cable felt like it was on the verge of melting. The cable I used came with the gateway and it had the standard ethernet connector on one end and the other end had both ethernet and USB options. I realized that I had plugged both into my computer. Could that have caused the overheating at the other end of the cable?
It sounds to me like you have a POE cable with some sort of extra USB connector. POE (power over ethernet). It may also be that the USB cable is meant to power an ethernet device plugged into the other end of the cable, possibly causing the overheating.
If you're simply using the cable to connect to your router, I'd recommend purchasing a normal ethernet cable with no added USB connections.