Sound Problem (Help ASAP, Please!)

So there’s this problem that I have, and I can’t figure out how to fix it. It’s with custom sounds, a sound doesn’t play, it’s completely silent. It’s the right bitrate, and the right file type, and it’s all in the right path. When I check the developer console, it says “Failed to load sound “(soundname)”, file probably missing from disk/repository”. This is really important, someone please help and tell me how to fix this. I’ve also heard about this problem before on other source games, but I haven’t found any way(s) to fix it. It’s impossible to test and hear my in-game sounds now. I’m pretty sure this only happens with custom sounds, because whenever I replace a sound, it doesn’t work anymore.

EDIT: OHH! I think I know when it started! Idk if this has to do with it, but the first case of this problem that I noticed was when I replaced all the M9K weapon sounds, and I couldn’t hear them. Later, I just started to notice when it got worse, which was when I hosted a server to play on with my friend, and I couldn’t hear the footstep sounds. Mayyybe when it all started was when I replaced the M9K sounds?