This tip will work for the following OS: Windows 2000, XP, Vista and Windows 7
Check the Speaker Connections and Volume Control Settings
Step 1 - Verify that the lack of sound is not due to faulty speaker connections. A simple way to test it is to substitute the speaker connection with headphones and see if you get any sound.
Step 2 - Open the volume control window by clicking your "Start" button and then "All Programs." Click "Accessories," then "Entertainment," then "Volume Control." Alternatively, just click on the speaker icon that's in your System Tray.
Step 3 - Check the volume and mute settings. If any of the mute check boxes have been checked, uncheck them. If this doesn't work, read on.
Perform a System Restore If Necessary
Step 1 - If the sound has been audible from your computer's speakers and is suddenly lost, you may need to perform a System Restore. Click on the " Start" button and then "All Programs."
Step 2 - Click on "Accessories," then "System Tools," then "System Restore."
Step 3 - Complete the System Restore Wizard. If this doesn't work, read on.
Step 1 - Deleting and reinstalling your sound driver may resolve the problem. Your sound driver may have been corrupted or may be missing. The result of this is that the restore utility menu won't be available. For Windows XP, follow these steps.
Step 2 - Click on your "Start" button. Click on "Control Panel" and then "System." Next, click on "Hardware," then "Device Manager, then "Sound, Video and Game Controllers."
Step 3 - Click on a sound device named in the Device Manager, and then press the Delete key on the keyboard. Click "OK" in the window that appears. Remove all the listed sound devices i this way EXCEPT Audio Codec and Legacy Audio Drivers.
Step 4 - Restart your computer. Reinstall the deleted drivers using the Driver and Application Recovery CDs that came with your Windows XP system.
Step 5 - Visit your computer manufacturer's official website. Check for any updated sound driver software for your sound card. If any, download them along with the installation instructions.