Windows_adjusting_sound_levels

Instructions are based on XP; your mileage may vary.

Double-click the speaker icon in the system tray (lower right corner):

This produces a "Master Volume" dialog box:

This dialog box allows control of the Output Volume.

To adjust the Input Volume, select Options->Properties from the pull-down menu. This results in a "Properties" dialog box:

Choose the "Mixer device" to match the soundcard that you are using, select "Recording" for "Adjust volume for", and click "OK". This results in the "Master Volume" dialog box being replaced with a "Recording Control" dialog box:

Make sure that the Microphone is selected via the "Select" checkbox. Adjust the levels to suit.