Trouble shooting TCP/IP connections
The most common network problems exist at the physical layer. Bad cables, jacks, NICs, or hubs constitute the majority of the problems found in the field. The first several things to try in most situations then, are experiments to isolate and check these components.
First, try the easiest solution, check that all the cables are firmly connected and in the correct jack. Computers and desks get moved, bumped and accidentally kicked. Most of the time this will solve your connection problem.
Not successful? Then swap your existing cable for a "known good" cable. This may be supplied by your FSP, or it may come from a functional AND co-operative neighbor. Some NICs (Network Interface Card, aka, ethernet cards) have a "link" light on them. This is a small (usually) green LED on the face of the NIC adjacent to the plug for the cable. When the machine is powered up, and the jack is activated, connecting a good cable should cause this light to turn on. This is a good sign that the physical layer items are in good working order.
If you cannot get a link light (and you have one), try plugging into another jack that you know to be good. If this does not produce a link light, chances are the problem is with your NIC. The final test would be to plug a "known good" machine into your jack and see if it functions correctly.
Obviously, if swapping the cable solves your problems, you know that the original cable was bad, and similarly if plugging into another jack fixes the problem, you can be fairly sure that either the jack wiring has gone bad, or the jack has not yet been activated.
Problem not solved yet? Go to the next trouble shooting page.