Can't find music files on phone anymore

[Dangaard]

I have a rather odd problem. Recently I went to go load more music on to my phone. I always drag and drop files directly to a music folder I created on the SD card of my phone (Sony Xperia TX) but this time I noticed that all of my music folders from A-D were there but everything from D-Z were gone! Confused I looked in my music player on my phone (Walkman from Sony) and was even more surprised to see that all of my music from A-Z was there. However, when I searched for the physical files from D-Z, I couldn't find them, despite searching for the files manually, using file explorer on my computer, using Astro file explorer on my phone, and using Sony's USB media syncing software. I should add that my search included both the internal storage of my phone and my SD card. Any ideas?