Please help me

i have a matsui mp3 and it was working fine until i accedently deleted the files. although the songs wont play, they are still stuck on the device. i cannot remove them with my computer. everytime i try it states 'cannot delete file' this is very inconvinient for me as i do not have room to put other songs on there. i now just have an empty mp3 player with nothing but 'deleted' songs on it. i am a music addict and it is very frustrating not being ale to travel with it as i have a very long journy to school. please help