If you know that the computer has a network card, but the operating system does not see it, you should check the BIOS settings. Restart the computer when system starts press Del or F2. To enter the BIOS can use other keys Esc, F1, F11, F12, it depends on the computer model.
In the opened window, locate the BIOS section that includes the word Integrated. In it find the line Onboard LAN Controller or something similar in meaning on different computers these lines may vary.
Let's see what value exhibited opposite lines found. If Disabled, the map is really off. Select Enabled and save the changes, usually to do this, press F10 or select Save and exit setup. After the computer restarts, the operating system should see the network card.
It is possible that the network card is disabled in the operating system. Open "start" - "control Panel" - "System" - "Hardware" - "device Manager". Look for "Network adapters". If the card is off, it will be marked with a red cross. To enable it, click twice with the mouse and click at the bottom of the window the option "This equipment is being used (enabled)". Click OK, network card is enabled. Connect it to the connector and try to go online it should work.
It may happen that the string network card will be marked with a yellow icon with an exclamation point. Most likely, the network card is not installed drivers. Try to install them from the installation disc if you have it or find it in the Internet. To reinstall again, double-click the line network adapter, select the tab "Driver" - "Update". In the appeared window choose "Install from a specific location" and open the folder with the driver. Click OK the drivers will be installed.