Ethernet (LAN) cable not detecting

Whenever I try to connect my ethernet cable which gives me internet connection its not being detected in my laptop. I rolled back from windows 10 to windows 8.1 few days back. My dell laptop model is Inspiron 15 (3521) . I downloaded the ethernet driver from the dell website and tried to install it. At the end of Installation it says " Realtek ethernet controller not detected" . Any help guys please.