Try to isolate your connection hardware (nic, hub, router)with a second computer if you have one so you can troubleshoot each to see if that is causing your problem. Just watching the little activity lights could give you a clue if it's hardware related.
I don't have a second computer to try the testing you suggesting.
However, all the lights on my cable modem are lit up and working properly, as they should. I even opened up a command prompt and released and renewed my ip to see if that helped, but it didn't change anything.