1. Go to Control Panel (click Windows Button - lower left corner, type CONTROL and click on Control Panel)
2. Type SOUND in the top right search box and click on CHANGE SOUND CARD SETTINGS
3. Click on RECORDING tab
4. Tapping loudly on or talking into your mic you sound see the sound level move on the mic level indicator.

If you have more than one mic attached to the computer you can Right Click and Disable different mic's on this screen

You can also Double click a mic then to go the LEVELS tab and increase the sensitivity.