Reset the network interface:

1. Disconnect the adapter from your computer.
2. Open System Settings > Network.
3. Remove "USB 10/100/1000 LAN" by selecting it and clicking the minus (-) button.
4. Plug the adapter back in.
5. Add "USB 10/100/1000 LAN" back by clicking the plus (+) button.
6. Open the Advanced settings and click "Renew DHCP Lease," then click OK.

"USB 10/100/1000 LAN" should now show as connected. If it still will not connect, shut down your Mac, wait 30 seconds, and power it back on. On Intel Macs you can also reset the SMC: shut down, hold left Shift, Control, Option, and the power button together for 10 seconds, release, then power on. Reconnect the adapter afterward.