Sometimes modems can be very problematic and can work on a day, and then due to various reasons, stop working without any further notice. In most of the cases, the only thing that can fix them is to actually reinstall all the software and the drivers.
If you're using a browser frame to manage it, then make sure the browser is supported and it doesn't use a PROXY to connect to a local address.
Additionally, install Net Framework and Visual C++ Runtimes.