No Internet Connection - Problem with Dimension 4400

I get an icon in the lower right-hand taskbar with the little yellow exclamation mark and a message that connectivity may be limited or nonexistent (it's nonexistent; I have no internet connection).  I can connect my laptop to the wall connection without any issues, so I think it's safe to say the problem is with something in the computer, not the ethernet cable or the router.  I have tried everything I can think of, including: (1) disabling/enabling the connection; (2) "repairing" the connection; (3) restarting the router; (4) replacing the network card and updating its drivers; (5) moving the network card to a different slot; (6) attempting to connect through USB using a ethernet-to-USB converter; (7) updating the chipset; and (8) replacing the motherboard battery.  So far, nothing has made a difference.  All my computer friends, as well as Verizon tech support, is stumped.  Any ideas?