How to reset your default media player to Windows Media Player
If you have installed Nero, PowerDVD, or other DVD playback software, and no longer wish to use these players, you can easily go back to Window’s built in Windows Media Player by simply uninstalling the desired software. However, sometimes a simple uninstall is still not enough. In such cases, please follow the directions below.
For Windows XP:
Go to Start, Settings, Control Panel, Add or Remove Programs. Then select “Set Program Access and Defaults” from the left panel. Click on the small arrow on the right near Custom, and find “Choose a default media player”. From there, you can select Windows Media Player as your default player of choice
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For Windows Vista:
Go to Start, Settings, Control Panel, Default Programs. Then select “Set Default Program”. Select Windows Media Player from the left side, and click on “Set this program as default.