You'll need to give us a little more information for us to help.. Operating system? Laptop or desktop? Age of machine? Which dial-up company?
WHERE in Windows does it say they're connected?
Is their connection cable hooked directly to the phone jack or through a phone recorder or other similar device?
Are you sure they used the dial-up ISP's installation CD to set up the connection? (Some such ISP's require their own install CD to be used to setup the account and connection.)
What have you already tried for fixing the problem? Tried disabling all firewalls to be sure it's not firewall related? Checked to remove all proxy options in Internet Explorer?
Hope this helps and let us know more.
My Grandparents just returned from Florida with their laptop, where they had a DSL connection. They are now back home with dial up and can't get IE or Firefox to navigate to a page ("cannot display web page message"). They say that there is a red "x" by the work offline option in the browser. They are connected through dial-up as they are getting emails through an email client and when they look at the connection in Windows, it says they are connected. My guess is that is has something do with moving from high-speed back to dial up, but it has been so long since I've touched a dial-up connection that nothing comes to mind and I'm unavailable to troubleshoot over the phone with them. Anyone know off hand how to take care of this?