Have you actually copied the songs files and folders to the correct target folder on your ps3? Check in the main thread what is the path and name of the target folder depending on whether you have the NTSC or PAL version of the game. If the songs show up in the game but don’t preview or load, it means the songs.dta file is in the right place but the songs files are not.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!