Ps3 wont play media from usb

Hello,
i moved all of my music, videos, and pictures from my computer and onto a memory stick, then plugged it to the usb for my ps3, it reads the usb and displays all of the labeled folders, but for some reason when i try and access the folders it displays nothing at all when the folder openes up, i tried pressing triangle for the display all option but all it does is give me more empty folders that dont work, why is this? and what can i do to fix the problem? thank you