try putting card into phone and power cycle (turn off then back on)
take card out and put into SD adapter then put that into usb card reader
open my computer and you should see your card as a new drive.
open new drive and there should be 4 folders, put your mp3, pix, flix, sounds that you want to put onto the card.
then put card back into phone.
see if that works, thats what you do for LG's it should be pretty similar for the moto's.