Atul,
Have you check to see if your audio drivers been installed? Here are the steps to open Device Manager.
- Press both Windows key + Pause/Break keys at the same time.
- In System Properties, click on Device Manager on left side.
- Check to see if your Audio device in Other Devices or in Sound, video and game controllers with a yellow exclamation point on any of those devices.
If they do have yellow exclamation point, run windows update or download Windows 7 drivers for your audio device from Dell website.