Memory stick problems

I got a memory stick pro duo 4gb last christmas and it isn't opening anything saved on it. my 32mb memory stick is working fine on my psp and my 4gb whas working fine until i tryed to pute a vidio on it a week or two ago. i had maby 60 songs on it, about 7 pictures, no vidios, and some saved data from my games. now when i try to lisen to music, view saved data, or look at som pictures, it says there is no photos, no saved data, and no tracks. but it says on my psp that there is 3870mb on it. i tryed puting a vidio on it befor and this never hapened.(i deleted the vidios after because they would show on my computer and not my psp.) i played one of my ganes on it and saved data on it to see if it would work and it did. (i deleted it after.) then i pute the 4 gb into the computer and deleted the psp folder on it because the files in the psp folder were gon, but it still says there are 3870mb left on it. my system software is version 2.81. how can i fix this?????