Sanyo Xacti won't recognise files on the internal memory

I plugged in my Sanyo Xacti to my computer and the files of the images came up on explorer. I navigated away from that folder and when I returned, the folder appeared to be empty. I have turned it off and plugged it in again, but then the files appeared named in wierd characters and couldn't be opened. When I tried again, it now shows the folder as empty.
According to the computer it's plugged into, the entire memory of the Xacti is full (ie no free space), but when you turn the camera on unplugged, and go to the images, it says "no images on file"
Does anyone know what I can do to retrieve the images?