1st of all you check the sound card driver is install in the system.and also know Manufacturer name .

• Go to the control panel
• Click on the System Icon
• Click on the Hardware Tab
• Click on the Device Manager then
• Click on the Sound, Video and Game Controller then
• See the Audio Driver is in the list.if it is available then
• Check the sound is it mute if it is unmute then
• Check the Speaker Cable it is inserted in the sound card
• If the problem is still exist then Reinstall the driver .
• Open the device manager and click on the Sound, Video and Game controller after this.
• After this Right Click on the Audio Driver the Click on the Update Driver and update diver wizard will start.and your driver will be reinstall if the problem is still exist.
• Replace the sound card or have a local tech take a look at the sound card.