The light is simply saying that the card has detected that a cable is plugged in. You need to look at the spec of the card to determine exactly what the red light actually means. Some stay lit even when the PC is switched off.
Goi to Device Manager and look and see if a Network card is recognised and working properly in its properties. Check that you have the correct and latest driver installed for the type of card you have installed. Can you let us know what type of network card it is.