Hi Denise,
The themes aren’t able to open as the default program has been changed to Windows Photo Viewer from default personalization CPL.
The Personalization CPL module allows interaction and changes to a Windows Theme programmatically. A theme is a combination of desktop background pictures, window colors, and sounds.
What we need to do is change the file format to open such themes using this module and see if it resolves the issue. Follow the steps:
a) Right Click on the downloaded themes file which you have saved on the computer.
b) Select Open With option and then click on Choose Default program. Check the box which says "Use this app for all .themespackfiles".
c) Click on Personalization CPL.
d) Double Click on the file and you would find the theme already applied and then the personalization window opening up on the desktop screen.
Please let us know about the results. We will be glad to assist you.