Xbox deletes files?

I had a USB stick with photos and etc. On it. I then put the stick in the Xbox to look at the pictures, but then the stick was empty. Then I put it in the PC and all the photos and data were gone.

Before plugging it into the Xbox, I put the stick in the PC and the data was on it.

Can someone tell me how I can get them back?

Note: In the end I saw the properties of the stick on the PC and there was the 3GB of memory used (these are the photos) but there was no data on it.

As with a USB stick, sometimes your files were simply formatted