e260 memory almost full, lost files, little space left, can't clear memory

I have a Sansa e260 Firmware version 01.00.15P

I had a lot of voice recordings that have suddenly gone missing.

The info page shows this:

Memory 3807Mb

Free 357Mb

Sonds 0

Voice recordings 0

FM recording 0

I have done afiles search in Win xp sp2 and the system cannot find any files of significance.

Properties says the same thing as the info page.

Used space 3.36 Gb

Free space  357 Mb

How can I free up space?

And are the voice recordings I had lost or recoverable?

Can anyone help?