Music Files Hidden in SD card, Unable to Read them.

I put some music on my motorola Gplay from my labtop, transfering files mostly mp4 or m4a and some of them cannot be red and my application google play doesn't see them at all.. they are confined in a section in my sd card and i can't copy them in the right folder(audio). Somebody already posted something really smilar to my problem and his username is L1nkOne but the answer did not help me at all. Thank you :^)