Well this is annoying...
I sort of went back a bit through notes here and wanted to determine whether it could all simply be a cable.
So I replaced the power cable. I then decided to try reinstalling Windows from an installer flash drive.
I am currently using Win10 again, on that SSD drive, and Windows has gone through its setup with no problems. I have yet to have any issues. Rebooted and rebooted several times while setting up Windows with no issues whatsoever. In fact, the system is flying, more than it was before but that could easily be either placebo or just coincidence.
So...
1. I've lost my last Windows. Pain in the ass. Any way I can do an instant relink of my former desktop shortcuts to their new drive location or is it a program shortcut by program shortcut job?
2. Why can't I give my storage drives the letters they have before? Disk management annoyingly won't let me choose those letters. I feel like it would make shortcuts easier to re-access.
3. How do I know FOR SURE that there is nothing actually wrong with this drive? I feel like I really need to confirm this before getting comfortable again with it.
Thank you, of course, all of you, for your input and guidance.