First check to make sure your Router is connected and sending a internet signal to your PC.
Then see if the Internet RJ-45 cable is plugged in securely. It might have slipped out slightly and not making a good connection to your RJ-45 Input port.
From your manual to determine if you are getting a Internet signal at your RJ-45 port:
Try a different Internet cable or use the same one you have now on another computer and see if it connects to the Internet.
Go to another computer and download your Motherboard's LAN driver and install it from a Flash Drive.
Possibly your motherboard's LAN Port went bad.
Check Device Manager under "Network" and delete the Intel LAN driver and restart your computer and see if you now have Internet again.
Once you restart your PC, Windows should install that driver again.