I don't know for sure what happened, but suddenly i could not even get into my Windows Photo Gallery. I Googled and tried some things, ran the FixIt tool and was finally able to open the Gallery and access my pictures. However, I can not open pictures within the gallery by just double clicking on them. I have to right click, select "open with" and then choose either "Paint" or "Windows Photo Viewer."
I set my default as Windows Photo Viewer. If it's set at Windows Photo Gallery the Gallery tries to open but fails and I get a window telling me it can't run and then it just closes down.