To retrieve data files in the folder of Pen/drive

I have usb memory stick 16GB that include many important data files. Yesterday, I connected it to my partner computer. After that, this problem happen. In my stick, I view folders and files. But I opened this folders, any data no have. And then " This folder is empty" appear. But I checked my disk property, the used space is no change (5 GB used). So What happen? where is going on my important data and how to get my data? Please answer to me.