This normally happens when your free trial and/or license have expired for some time. 

• If you think this machine should be licensed, check to see if your Ethernet connection in the Network Connections control panel is disabled.
  • To re-enable on Windows, go to Start -> Control Panel -> Network Connections, right click on your disabled connection, and select "Enable".
  • To re-enable on Mac, open Terminal, become root and type:
    sudo ifconfig en0 up
• If you want to work without a network connection for security reasons, you can unplug the network cable but still leave the network adapter enabled.