Take a look at these troubleshooting steps. Unfortunately, for users of Microsoft Vista, changes were made to the audio controls for wired microphones, but there are steps you can take to fix the problem.
1. If you are having trouble using your microphone, first verify whether the microphone is recognized by the operating system. If you have plugged in an external microphone make sure it is plugged into the correct port and that it is fully inserted. If the microphone is plugged in check to make sure it is enabled in the operating system settings. Click on Start in the corner of your computer's desktop, go to Control Panel then click Hardware and Sound. While in the Hardware and Sound window click on the Sound section and then select Manage Audio Devices. If you see your microphone available, click on it and enable it. If your microphone is not recognized make sure the audio drivers for your specific microphone are installed. Also ensure that you have the current drivers for your computer's audio card.
Confirm Working State
2. If your microphone is plugged in and enabled you should test the device using Vista's built-in sound recorder. Connect your microphone and click Start on the desktop. Select All Programs from the menu, then Accessories and click Sound Recorder. Start recording and test whether the microphone will pick up your voice. To use a sound recorder you will need to have a sound card and speakers installed on your computer. If you are using a program such as Skype for voice chat, these applications have built-in microphone tests that you can use.
3. A non working microphone can be an indication that its preferences are not set up properly. Go to the Sound section of Hardware and Sound and select the microphone location from the areas shown according to where your microphone is plugged in. Make sure the microphone is enabled and click the Levels selection from the Mic Properties dialogue box. Move the microphone slider all the way to the right, and move the boost slider to the required level, too. Click on Apply to set the new changes. If you want these to be the default setting for the microphone, click on the Advanced tab and click on Default Format. To change the current setting to the default, change the settings to Exclusive Mode and then click Apply.