You can use the line-in connection on your sound card to connect a portable music player, microphone, or other audio input device to your computer.
However, the line-in connection to your sound card is muted by default. This means that if you plug an audio device into this port, it will not produce any sound on your computer until you enable sound for the line-in connection.
Open Audio Devices and Sound Themes by clicking the Start button , clicking Control Panel, clicking Hardware and Sound, and then clicking Sound.
Click the Playback tab, click Speakers, and then click Properties.