How many folders and sub-folders did you put on the storage device? The PS3 only supports a series of one folders. In other words, you can't make a folder for the Artist and a sub-folder for the Album. Either that or the music you put on the thumb drive is not compatible with the PS3.
On your USB drive (flash drive) you need to have a folder called PS3, inside the PS3 folder create another folder called MUSIC. Now you can put your music files inside the MUSIC folder. Make sure there are no other folders inside of the MUSIC folder. I used all caps for the folder names and it works for me. You can also put folders inside the PS3 folder called VIDEO, and UPDATES to use for video files or system update files that you can download from your PC instead of updating from the PS3. It is faster to update using the computer. Your PS3 should recognize your music files once they are put into the MUSIC folder inside the PS3 folder. Good luck.