This looks like the media scanner messed up its database. I recommend to:

1. clear the media storage (see [the middle of this page][1] for details with screenshots):
    1. go to *Settings › Apps › All*
    1. find "Media Storage" and tap the entry once to open the app details
    1. chose "clear data" (to empty the media scanner's database)
1. reboot

On device startup, the [media scanner](https://android.stackexchange.com/tags/media-scanner/info) will be triggered to run, and should – this time cleanly – build up it's database.

**Note:** If you've customized ringtones/notification/alarm sounds, you might need to redo that afterwards as the association might be lost.²

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<sup><b>²</b> Applications identify those sounds by an ID, not by directory and file name. With the new buildup database, those IDs no longer match.</sup>


[1]: http://www.jrtstudio.com/iSyncr/Tutorials/How-To-Refresh-Android-Media-Cache "Refreshing Android MediaStore Database"