Did you exclude the folder? If you excluded it, open up media>menu>options and go to the "exclude folders" button and uncheck the folder if it's there.
Open media player then menu then explore navigate to navigate to folder file is in hit menu and then show hidden.
If the file is on your media card u can also hook BB to your computer make sure windows is set to show hidden files. Find the file right click it choose properties and then uncheck hidden box.
Posted from my CrackBerry at wapforums.crackberry.com
You have to be in the folder it is in for it to show up on the menu. For example if you got to blackberry pictures and there is a hidden folder in that directery show hidden will show up in the menu.
Posted from my CrackBerry at wapforums.crackberry.com
Take a look at the second to last post by ACE he breaks down where you should be able to do this from the device. Key is you have to EXPLORE then push in menu to show hidden, once you find the hidden folders you can then unhide them.