modem issues

I have a modem problem. I have a 56k v.90 modem and appeard to be working ok at first. Now when I click on the connect tab of my ISP provider, I can hear my modem dialing out trying to connect. However, after many attempts of modem dial out I’ll get error message 629 “The Port was disconnected by the remote modem or could not establish a connection by the remote modem”. I even tried using different access numbers and still have failed attempts. If anyone has a solution to this madness please respond.