Run an ipconfig first and check to see if the address is valid. If it is check that the drivers are up to date, you can do this by using a flash drive to upload the drivers. If that doesn't solve it you could go to Network and sharing center and go to change adapter setting to make sure that is on and running. You could also try deleting and reinstalling the Ethernet/WiFi via Network connections in settings. You could also look for physical buttons some machines such as Dell Lattitudes E6440s have buttons on the side that you can slide over and put it in airplane mode, also make sure airplane mode isn't on. Their is a number of other ways to do it but these would be the basics.