What is your "Elements 10" program? Photoshop Elements or Premiere Elements? Or are you in the Elements Organizer 10 which come with either Photoshop Elements 10?
What video card/graphics card does your computer use?
Let us start here so that we can begin the troubleshooting for the project that you are using.
Any questions, please ask.
Photoshop Elements 10
If your program is Photoshop Elements 10, please re-post your thread in the Adobe Photoshop Elements Forum to take advantage of the specialized expertise there. Some how your thread got posted in the Premiere Elements Forum (video editing).
I have used Photoshop Elements 10 and the Elements Organizer 10 that comes with it on Windows 8.1 and 10 64 bit without issues. It sounds like the thumbnails are running into problems updating. What computer operating system did you use before this? Did you upgrade from Windows 7 64 bit to Windows 8.1 64 bit on the same computer? Or, are two different computers involved for the before and now? The Photoshop Elements Forums experts should be able to sort through the details to find a solution for you. If you do not get an immediate response there in this matter, please let me know, and I will put on my Photoshop Elements 10 hat and try to find an answer based on your details.