Recently bought a mp4 player

Question

recently bought a mp4 player whilst on holiday in lanzarote its called cyber-sound (1gb)when i got it home i looked at the instructions and they just didnt make sence (badly translated) so i just did wat i did with my old mp3 player and copied from my downloads and then pasted in to removable disk this seemed to go fine until i went to play them on the mp4 i went in to music to look for the files and it came up with EMPTY DISK! any help it solving this would be great thanx in advance