Well it may not be the audio itself. It can be per program. Many programs have their own options. So you would need to change the settings in each one you are using to make sure they are not the cause.
Once you have ruled that out, try the following..
1. Go into "Control Panel", click on "Hardware and Sound" and then click "Sound".
2. Make sure you are on the "Playback" tab and right click on "Speakers". (Yes, I know you said microphone not speakers.)
3. In the list that pops up, click on "Properties".
4. In this new window click on the "Levels" tab.
5. Locate your microphone in the listed levels and adjust to suit your needs. Then click "Apply" and finally "OK".
You can close all the opened windows and you should have them set to...