Can't add more songs on MP3 player even if thers more space?

Ok so my mp3 player has 1 GB space, and it worked well so far, had it for about a year or two. But now i dont know why, since the last time i Fast Formatted it ( deletes all my songs ) there's a problem. I can't seem to be able to put more than 653mb worth of songs, as if the rest of the space didnt exist anymore. It says Error: cannot creature file or folder. =/ I usually upload using explorer with a USB cord..

Model: Sandisk Digital Audio Player 1gb