modem problem

[kjservices]

i have a hp laptop running windows xp and have a problem with the internal
modem
when i go to device manager it reports that the modem is installed
correctly - and when i test the modem it responds ok, but when i try to
connect to the internet i get a no dial tone response
i have tried different phone lines, different internet accounts and
different phone cables but with the same response - i have also installed an
external modem and this works fine with the different phone lines, internet
accounts and phone cables
is it possible that the socket where you plug in the phone cable is damaged
which means that as far as the computer is concerned the modem is
functioning ok?

any help would be much appreciated

andrew