You have to check if your sound card is working properly.

1. First, right click my computer and click on properties. Choose devise manager. Click on sound,video,controller. From here you can see if your devise is working properly.

2. If working properly, click on control panel (found in start menu) and select sound. adjust your settings.

3. If sound card not working properly, check if you can update the drivers. This can be done from point no.1.

Hope this helps.