You see that little icon down in the lower right area of your kicker panel that looks kind of like two plugs? Right click on it and select connect to eth0. Anytime I've had this issue in the past, that has been the solution for me. Going from one place to another place seems to bring up this issue at least once. After that 1 time event, the problem doesn't seem to happen again, well, most of the time. Another way would be to turn-off the wifi on the laptop, connect the Ethernet cable and boot-up from complete off condition. Boot should detect the live ethernet cable and settings automatically. I've noticed this problem on several distrobutions, they want to connect the same way again. You go crazy thinking something is broke and troubleshooting for an hour.
Most ethernet ports have a little activity led built-in, check to see if there is activity, if not maybe you have a bad cable?
You have your way. I have my way. As for the right way, the correct way, and the only way, it does not exist.”
- Friedrich Nietzsche