Then if I click on the networking icon, I just see text that says Networking disabled.
Thankfully, this is a relatively easy fix. Run the following commands:
sudo rm /var/lib/NetworkManager/NetworkManager.state sudo service network-manager restart
When the service starts up again, that file will be re-created with the property NetworkingEnabled set to true. Of course, you could avoid deleting that file and just modify the property yourself – setting it to true – but I feel it is quicker to just remove the file and restart the service.