Testing Network Cables
If your computer can't communicate with any other on your LAN, and the Device Manager doesn't indicate a faulty network card, you might have a wiring problem. Wiring problems can be the most difficult to solve because it's difficult to prove that data is leaving one computer but not arriving at another. The ping program, discussed later in this chapter, can help with this problem.
To learn how you can use the ping command to diagnose Internet-related problems, as opposed to LAN problems, see "ping," p. 547.
If your computer is not properly wired into the LAN, in many cases, Windows displays an offline icon right on the system tray and indicates that your network card is disconnected. It might not, though, so you shouldn't take a lack of this kind of message to mean that no wiring problems exist.
If your network uses UTP cabling plugged in to a hub, there's usually a green LED indicator on each network card and at each port on the hub. Be sure that the lights are on at each end of your network cable and those for the other computers on your LAN.
You also can use inexpensive (about $75) cable test devices that check for continuity and correct pin-to-pin wiring order for UTP wiring. They come as a set of two boxes. One gets plugged in to each end of a given cable run, and a set of blinking lights tells you whether all four wire pairs are connected and in the correct order. (If you install your own network cabling and/or make your own patch cables, these tools are handy to have to check your work.)