Music discs not working after working perfectly fine.

I made a mod that adds 5 new music discs, as well as new mobs, items, biomes, and recipes. At the time i made the discs, i had a biome, a mob, a new block, a new fluid, a new dimension, and a new food. I tested the music discs (They are an .ogg, mono, and selected as music) and they worked flawlessly. I added more things to my mod, such as new structures, mobs, and items, and i tested the discs and they just stopped working. They were working perfectly fine before, but now they dont play any sound at all. Not even the subtitles appear for them. What do i do? These discs are one of the mods big features and i really cannot scrap them...