Go to Web Admin, in Files&Media->Media Files Sync page select audio from the left frame(home-public-data-audio) and press the Resynchronize button. Then go to each subdirectory where you've stored music. If one file isn't in the LMCE database it wil have "Type:" drop down and "Add to database" button next to it. Select it's type (generally for audio files select LinuxMCE Audio FIle_, press the "Add to database" button and after you've added all your files press again the Resynchronize button.