The problem:
1. You are seeing a red x near your speaker icon.
2. When you move your cursor atop the speaker icon, you get the message “No Audio Output Device installed”.
The solution:
First, don’t panic. There is a good chance that your audio output device has only been disabled and not been uninstalled. If it is disabled, simply enable it and it will work. Here’s how to do it.
Right click on your speaker icon and choose ‘Playback Devices’. Your speaker should show as disabled. Right click on Speakers and choose Enable. Your audio should be restored successfully.
Sometimes, if your speaker is disabled, it may not show on the window like this.
In this case, right click inside the window, and choose ‘Show Disabled Devices’. You should then be able to see the speakers. Right click again and choose ‘Enable’.
Now, if your speakers weren’t just disabled, you may have to try upgrading the drivers. If that’s the case, do the following.
Go to Start – > Control Panel -> Device Manager.
Look for Sound, Video, and game controllers. Click the + on the left.
You should see your audio device listed. For me it was High Definition Audio Device. It could be others like Realtek Audio Device for you. Anyway, right click on the audio device and select “Update Driver Software”.
If your audio device was previously working, but not working now, you should be able to update the driver software from a local directory or from the Windows Vista CD. So choose ‘Browse my computer for driver software’.
Select “Let me pick from a list of device drivers on my computer.
Select your audio device driver from the list and click ‘Next’.
Choose ‘Yes’ when the update driver warning pops up. Once the driver is updated, your audio device should start working again!