I started this thread and came up with a solution that worked for me and may work for you if you are having the same problems with your mic.
1. I uninstalled my sigmatel drivers (Vista - go to control panel - programs and features - double click sigma tel to remove)

2. Go to
Drivers and Downloads
(if you have a dell) and download all the audio drivers and all the chipset drivers (i downloaded and installed 2 audio drivers and 2 chipset drivers for my Dell E1505)

I am not a computer wizard and don't even know if this is the proper way to do things, but my mic now and I am happy.

I think the solution is to uninstall your audio drivers, re-download and reinstall them.