A day later. I think I have found out what was wrong with this computer.
It seems I may have fried two hard drives in this machine. The one that contained the Linux Mint OS, and the 500GB drive I use for downloads.
Consistently booting were the main 320GB drive that came with this computer 5 years ago when I got it used, and the 3 drives that contained movies and tv shows. It would appear that the 500GB drive is toast, as well.
I have a back up solid state drive, and I may end up using it. But to get this out the door, I decided to re-install Linux Mint, this time on the 320GB drive that is 8 years old and still runs like a top. Funny how the older drives are often more hardy than the newer ones. But I digress.
I have successfully reinstalled Linux Mint. Now, I have to go through the effort, in the coming days, to reinstall all the apps I like, like dropbox, and Abiword, and Gnumeric, and another browser or two. Oh, yes. And let's not forget Plex.
After I finish this blog post, I will take the SSD out of the computer and see if I can find an enclosure for it. If I can get it working after all, then I will be flummoxed as to why the machine won't boot with it any more.
But, hey, at least the computer is up and running again. That should count for something, eh?
The Flash starts in a few minutes. See you tomorrow.