If you can't see thumbnails for your raw files—and you're using Windows—read on.
You probably can't see the thumbnails because your computer doesn't have an up-to-date codec for the raw files.
A codec compresses large files to save space.
Then, the codec decompresses the files when you open them up.
compression - decompression = codec (or coder-decoder).
Do the following to get the up-to-date codec.
1) Go to the website of your camera manufacturer.
2) Search using the term codec.
3) Download the codec for your camera brand and model.
Search for the most recent codec download, such as:
FastPictureViewer Codec Pack Not free