Go to Control Panel -> Network and Internet -> Network Connections -> Right click your Ethernet adapter -> Properties -> Highlight "Internet Protocol Version 4 (TCP/IPv4) -> Properties -> Check if both settings are set to Obtain Automatically -> If not then set the two radio boxes to obtain automatically -> OK -> Test your internet if it works.
If it was already set automatically and it didn't work there might be many other problems, so you might want to give us more information, like your Ethernet adapter name, and what does the warning message say.