I downloaded the Advanced MP3/WPMA Recorder (Don’t worry: this is a link to the review, not the download) from download.com, and my microphone worked as I used this. Shortly afterward, I downloaded Sound Forge by Sony–also from download.com–and my microphone wouldn’t work with this or Windows sound Recorder. Could it be one of these programs that caused it? Or is there another explanation for microphones abruptly ceasing to work? The mic is external, btw.
Did you check to make sure the microphone didn’t simply revert to its default state (Mute)?
You say it won’t work with Windows sound Recorder or Sound Forge, does it work at all with anything?