Hi Regedit32. Your post gave me an idea. I went to the store as you instructed. I clicked on my account icon, but "sign out" was not among the available choices! I reasoned that this is because I have my computer set up with a password that logs me into my Microsoft account at the same time that it logs me onto my computer. So I reasoned that the only was to sign out of the store, was to sign out of my computer. So I just shut down my computer. Problem was, it wouldn't shut down!! It wouldn't restart!! I would get nothing from the start>power>shut down command at all. If I hit CTRL-ALT-DLT and called up task manager, and then used the power icon in the lower right corner, I could at least get it to try to shut down. I would get the orange screen and the scrolling circle of dots. But after about 3 - 5 minutes, the desktop would reappear. Same thing if I tried the Restart command in Task Manager. Then I tried to get on the internet to do a post here, and IE would not work. Neither would Edge! So I did a hard power off with the power button on my computer. After a five minute wait I powered it back up and after this reboot, guess what. IE and Edge work, and so does Store and I can now install apps!!! I generally leave this computer on and connected to the internet all the time. I put it to sleep when I am not using it, but by leaving it on, it keeps itself updated. But it seems that just like in the old days, it may be a good idea to completely shut it down and reboot it every once in a while. Some "stack" somewhere gets overloaded with stuff that it won't release, or resources are tied up, or something. Anyway, problem solved and your post led me down the path, so I am marking yours as the answer.
Thanks