Mp4. I've got a 2 gigabyte mp4 and it worked fine for the 1st few weeks after I got it and about 3

Question

I've got a 2 gigabyte mp4 and it worked fine for the 1st few weeks after I got it and about 3 or so weeks ago I added more music to it but then deleted 1 song and now whenever I press to go into the music or video section it just comes up with Empty Disk! But when I plug it into the computer and press 'view files' a list of the files that are on it come up. it's EXTREMELY frustrating.
I'm not sure what brand it is as it doesn't say on the box, mp4 or in the instruction manual.
the box is gray with some lady on it with a patch of straightened har hangin' down.
I've tried deleting all the files off it through the computer but that doesn't make a difference.

=(