Power Cord Question

I have a Latitude C610. The power cord that goes from the wall socket to the big black square thing with the little green light works fine, and the green light is always on. However, upon plugging it into my computer, it does not produce a charge to the battery. It did on and off for a while, and now no longer does. One interesting thing that I see, is that when I look at the three little holes in the plug that goes into my computer (which actually have the numbers 1-2-3 next to each one), I see little metal pieces inside two of the holes, but the third hole does not have anything metal inside it. I don't know if its supposed to be this way, or if this could be the cause of my problem. I am trying to find someone with a Dell laptop that uses the same type of connector to test, but in the meantime I thought I would ask if all three little holes on the plug should have metal visible inside them? Any advice is greatly appreciated!