I could see and open .jpg and .png for example in Windows 10. But when I opened MS Photos, no thumbnails would show and I couldn't open them. I did search the internet and tried all recommended solutions with no success.
I then remembered when I set up Windows 10, I went through privacy settings and under pictures disabled "allow access to pictures library on this device". After allowing access again, the thumbnails would show and open.
I hope this information will help those with this issue.