How to Restore System Default Soundsby Mike Benson
Sound themes in Windows are a collection of sound files assigned to various events that occur in Windows and other programs. When you install and set up Windows for the first time, the default sound theme is applied. However, over time a program or user may have changed the sound theme. If you would like to reset the default system sounds in Windows, you can do so from the sound properties.
Press the "Windows" and "R" keys simultaneously to load a Run box.
Type "mmsys.cpl" and click "OK." This loads Windows Sound and Audio.
Click the "Sound" tab.
Click the drop-down menu under "Sound Scheme" and select "Windows Default."
Click "Apply" and then "OK" to save the changes.