If you open the NAS with your file explorer:
- Is the directory structure intact (ie, can you see the directories you have set up?)
- Are the size of the files (and possibly their time stamps) coherent with what you know of them
- Can you open the file with any kind of image viewer (try several image applications, you can always open the files in Firefox/Chrome)
- If you use the explorer to copy a files form the NAS to the local disk, does the copy occur without any warning/error message? Is the resulting file the right size? Can you open it in an image viewer?
If the answer is no to any of this, the best course of action is to stop the NAS, and bring it to someone with some computer experience.