If the ethernet port is on the motherboard, and there are no lights on it, I would check to see if you have the driver disc for the motherboard.
There may be an option to install the ethernet drivers and this could fix the problem.
Alternatively, make sure the cable is properly plugged in at both ends, from the PC to a router/adaptor/switch.
If it is still not working, try a different cable.
If you still aren't having any luck, there is a small chance that the port is damaged and no longer works...