ethernet port

[KEVIN Lock]

It would seem that I have a dead ethernet port on an eMac.    I have 
changed cables to the ADSL modem and still no joy. The modem is OK 
and shows a connection on a PC laptop
Any advice for me here?    What can I attach to the cable to 
positively determine that the port is the problem?
And if it is the problem, is it worth fixing?

Thanks in advance,
Kev