ethernet port not detected

[mandid12]

I have an emachine 210 pc and have recently obtained a router/modem which I can't install. The internet is working and the pc is too but the pc doesn't seem to be picking up the modem despite all the leads being in the correct ports etc. In playing the istallation disc the error message says 'no ethernet port detected' Can anyone help?
Thanks

[ACtheTROLL]

you don't say which os ... so look in device manager for the nic

if not working - probably drivers

if ok
open commant prompt - type ping 127.0.0.1
then ipconfig /all
enter between each command

come back with results