I assume it's internal then?

You didn't reinstall drivers for anything recently, or Windows, or install any new hardware or change any hardware settings lately?

I'd also say check the settings for the COM port the modem is on (probably COM3 if it's internal) and make sure that's at the right speed i.e. 57600 or 115200 bps - that's probably floating around in Device Manager somewhere. And when you talked about the buzzing, maybe you turned the modem speaker on and used to have it off all the time before? I always had the speaker on when I used to have a modem just to hear the dial tones as it connected - it'd always buzz after the dialtone for the ISP number, before going silent once actually connected