After Microsoft's install is done, it's left to the installer (you!) to install drivers for motherboard, video, audio, USB, modem, printer and what have you. Many only learn that Microsoft provides the OS, and you provide the rest after they format.

Generic modem drivers rarely work today. You'll want to find the proper driver for your modem. But motherboard drivers are likely needed before that works for many systems.

You didn't tell about the machine, so no one can help you find said drivers.