I have Windows 8.1 and it does not show any thumbnails. I've cleared the thumbnail cache and checked the view settings and they are both set to show thumbnails.

Any ideas?

Check : https://social.technet.microsoft.com/Forums/en-US/50a9576c-65fc-4af1-a77f-f3cfb42c1871/windows-explorer-is-not-displaying-thumbnails-as-it-was-earlier-instead-it-is-showing-default?forum=w7itproui

https://social.technet.microsoft.com/Forums/en-US/a8c0080a-10c8-49e7-8602-d65669369a1a/windows-explorer-thumbnail-preview-disappeared?forum=w7itprogeneral

I've already tried both of those solutions but it hasn't corrected the problem.

Hi,

Have you make any change to your system before this problem occures? Especially install new program.

You can try to perform a Clean Boot to check whether this problem caused by 3rd program or service start with system. Refer to the link below for more details.

http://support.microsoft.com/kb/929135

If problem persists, try to use ShellExView to check if there is any 3rd extension of Windows Explorer that may cause this problem.

ShellExView:

http://www.nirsoft.net/utils/shexview.html

Sorry for the delayed reply. When I did the clean boot my media file started showing the thumbnails but I still don't have thumbnails for document files like Word, Excel, and .pdf files. I'm having a little trouble figuring out how to use ShellExView.