If the LAN is turned on in the bios and you get no light on it at all when you plug in a cable it may be dead. Can you see anything about it in the device manager and did you install the chipset and LAN driver?
If the onboard dies you need to add a PCIe card or USB adapter, although for wired I greatly prefer the PCIe card.
I usually use
THIS ONE[/b] as Intel is highly compatible and keeps its drivers up to date.