Have you tried System Restore to fix the problem? This is an invaluable tool. Using it will not result in any loss of personal data and they can be undone if not helpful.
In Vista "System Restore" is accessible from the Start Menu. When it opens you can select NEXT > and choose a date prior to the problem. You may need to check the box to show restore points older than 5 days. If you choose not to keep the restore, run it again and select the "undo" option
As for using another application to play Audio/Visual files, I would recommend:http://www.videolan.org/vlc/