Small issue that is bugging me.

[Big Booger]

Did you try opening the folder where the content is stored, then clicking tools/Folder Options/File Types/

Then selecting the file types you want to change, select advance and then choose the product you want that particular type to open with?

I doubt this will work seeing as almost everything you've tried has failed, but it is one other way to do this.

as for the tumbnail, again go back to windows explorer, click tool/folder options/View

This time try resetting all folders, and then apply to all folders.

Then restart the PC. It may work, then again it may not.