Modem Dials but Doesn’t Connect

I am having trouble with a modem, it will dial but does not connect, after awhile you will hear a sound that sounds like you left the phone off the hook. The phone line has been checked and it is fine. When I try to connect it says a cannection cannot be established or the server is not answering but the internet provider says it is OK that it has to be something in the computer causing the problem.