For various reasons, you may want to change microphone settings in Windows.    For instance, a webcam microphone may be the default microphone instead of a USB dedicated microphone, or your volume settings may be too low.  Changing these settings is simple and easy in Windows 7 (note that these instructions also apply for Vista users).

1.  Navigate to the Control Panel (Start button -> Control Panel).  Click on the "Hardware and Sound" link in green.

2.  Click on the "Manage Audio Devices" link under the Sound section.  

3.  Click on the "Recording" tab.

3.  Here you can choose which device is your default microphone, which is the microphone which will typically be used by most programs.  To adjust volume and other properties of each microphone, highlight the microphone and click the Properties button.

3.  On the Levels tab, you can adjust microphone volume.  You can also change other properties in the other tabs, feel free to play around!