Microphone Issues

I've got Windows Vista Premium running on my Dell Inspiron 1501.

I have a headset microphone that I run in Teamspeak and Adobe Audition. The mic originally worked. Every time I plugged it in to the microphone jack, I would get a pop-up asking me what the line-in was (Microphone, Speakers, etc.). This was rather annoying, so after about 2 weeks of selecting the line-in, I checked the little box requesting that it no longer come up. Since then, my microphone has ceased to work. I have gone into Sound and Audio Devices, and checked my microphone. It says the drivers are installed and the device is enabled. According to Vista, there's nothing wrong with it. Obviously, Vista is wrong. How can I get the annoying little pop-up box back, and/or how can I fix this? I need my microphone for work.

If this is the wrong topic, please let me know so I can post it in the right area.