What if your memory stick occupies space but there are no files?

There is a few things to this... a 4gb stick isn't necessarily 4gb's as it is an approximation but it should be around it (usually in the 3990's of mb's).

If you are reading it on your computer and don't see any files, go into properties (right click on the white of the memory stick window) and it will show memory available and memory being used.

If you are reading this on the psp you got several possibilities. You A. have put the wrong format of the file in your psp. You have put the right format file in the wrong folder. Or you got a brand new clean memory stick which in that case go into the psp and look for the option to format the memory stick.

About 9/10 you just have to format your memory stick via the psp.