Returning with an update in case it might be helpful to anyone else facing this issue.
First, thank you to NancyWyman for the detailed instructions about uninstalling the driver. I may yet have to use them! But since the Surface is still under warranty, I did eventually take it to the Microsoft store when I had other reasons to go to downtown
Toronto. Of course, that day it played videos perfectly... But I described the problem, and another one that had cropped up by then, which was that the Surface's internet connection would quit randomly while other computers in the house stayed connected.
The technician installed Chrome and updates that were apparently waiting to be installed--I had thought that they installed automatically. He suggested it might work better with a docking station. Since that day it has played videos, but still dropped off
the internet occasionally. I bought a docking station online for much less than it's sold for in physical stores, and that seems to have stopped the internet dropping problem.
For those who advised me to throw out the Surface and buy something else, I can say I've been tempted! But there's a lot I like about it. I travel a fair bit and though it's light, I can get work done on it as well as I could with my heavier Sony laptop.
Also, as a fast touch-typist of a "certain age" I haven't been able to adapt to the Canadian bilingual keyboard which is on most less costly laptops these days; the Surface type cover has normal-sized shift and enter keys. I wish Microsoft hadn't discontinued
it.
Thanks to all who replied and for those sticking with their Surfaces, please keep sharing tips to keep them working.
The bottom line is that it is junk. Got rid of mine months go. uninstalling the drivers did nothing.