I have to guess you are writing about Explorer and how it might or might not show thumbnails. Said thumbnail is rendered by Explore working with a "CODEC" and can fail. If you forget the thumbnail and associate the file with VLC Player then you should be able to double click to play it in VLC Player.
You bring up a great issue with Windows. That is, after over a decade folk are still befuddled with the video CODECs. Do you think it's time for a new OS that doesn't have so much for the owner to deal with?
Bob
I downloaded VLC to compliment Media Player 11 and it was a disaster to my system . Now I have it all cleaned up but at one point thumb nails were inaccessible. The only thing left I can see is that my system wont start up a video on one click. I have to click open with and at the top of the options is the word Shell. What is going on ?

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