If this is a wired network, verify that the network cable is properly connected and make sure the LEDs next to the network jack are properly illuminated. For example, a network card with a solid green LED or light usually indicates that the card is either connected or receiving a signal. If the green light is flashing, this is an indication of data being sent or received. In the picture is an example of LAN port with two LED indicators next to the RJ-45 port. With this port, one LED will light up if connected properly and the other will flash when transmitting data.
If there are no lights or the lights are orange or red the card may be bad, not connected properly, or that the card is not receiving a signal from the network. If you are on a small or local network and have the capability of checking a hub, switch, orrouter verify that the cables are properly connected and that it has power. If after checking the connections the LED indicators appear bad, the network adapter, port, or cable may be defective.