Why can't music players find my audio files?

On my Nexus 4, there's a folder called /sdcard/Music/ (or just /Music when browsing the phone's storage; Windows 7 calls it Computer\Nexus 4\Internal storage\Music) and I've put a lot of songs in there but **the music player doesn't see any of my songs.** Why can one app (the file manager, and e.g. Dropbox) see the files, but not another app (Play Music, Apollo, Jukefox)? **Notes:** - LG Nexus 4 16GB, unlocked, with CyanogenMod 10.1 (nightly build 20130212 because nothing *more stable* is available but there are no crashes.) - The songs are stored in the path format /sdcard/Music/Artist/Album/Song title.mp3 (simply because that's how they're stored on my media drive). - Computer\Nexus 4\Internal storage\Music\Eagles\On the Border\1 Already Gone.mp3 - Computer\Nexus 4\Internal storage\Music\Kashmir\The Good Life\10 Kiss me goodbye.mp3 - Computer\Nexus 4\Internal storage\Music\Christina St眉rmer\Freier Fall\1 Geh nicht wenn du kommst.mp3 (yes there's a Chinese character in there and I don't know why; it's a German ü *(umlaut u)* on my original Windows media drive) - I know that the songs are present and that they work because the CyanogenMod File Manager shows them and I can play them individually. *They do exist!* - Running Rescan SD as suggested below didn't make the files appear in any of the player apps. - I'm fairly certain there are no .nomedia files: The CyanogenMod File Manager doesn't display files that begin with a . (I renamed an existing TXT file and it promptly disappeared :)) but I used the Root Browser Lite to look through /Music and subfolders -- the only match I found was the one I had renamed, and I have deleted that now. - My Windows pc at work couldn't see the files either, but after unplugging/replugging the USB it now can see+open+play the files. (I've now revised this question to remove the Windows part.) - I'm still mystified by the fact that file-browser apps see the files but music-player apps don't.