Please link Realtek website to download the latest LAN driver to fix it, and follow the SOP to know how to install new driver correctly.
Realtek Website :
http://www.realtek.com.tw/DOWNLOADS/downloadsView.aspx?Langid=2&PNid=13&PFid=5&Level=5&Conn=4&DownTypeID=3&GetDown=false
SOP :
1. Uninstall old LAN driver first, and install new one completely from OS, then shutdown OS
2. Take off AC power
3. Wait 1 minute
4. Re-plug AC power, then press ”power button” to power on the system.