If it was just a faulty cable, it should just connect without the need for any user input… and you shouldn’t be asked for a password to get a network connection.
But just in case the network settings are somehow messed up…
Open the network manager, by right-clicking the networkmanager icon (by the clock):
http://linuxforums.org.uk/MGalleryItem.php?id=1351
and select “Edit Connections”
Now on the “Wired” tab, highlight any connections and select “Delete”… until there are NO connections.
Click “Close”.
Normal (left-click) the networkmanager icon, and select “Auto Ethernet” … you should now be connected.