As porkop said, try re-installing the audio drivers... regardless.
If no luck there, follow what Tiny posted about running System File Checker.
If that doesn't sort it, you may have to locate and correct a file in the registry.
If that doesn't work, then it's re-install windows 7, upgrade to windows 10... or just live without the sounds.
As I mentioned, I turn all my windows sounds off.
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