This looks like the media scanner messed up its database. I recommend to:
- clear the media storage (see the middle of this page for details with screenshots):
- go to Settings › Apps › All
- find "Media Storage" and tap the entry once to open the app details
- chose "clear data" (to empty the media scanner's database)
- reboot
On device startup, the media scannermedia scanner 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
² Applications identify those sounds by an ID, not by directory and file name. With the new buildup database, those IDs no longer match.