Restoring Inspiron 5559

I currently own 3 Dell computers. My Inspiron Mini HD sat idle as a backup for 2 years, When I turned it on this summer, it promptly updated to the most current version of Windows 10. It has become slow but otherwise works fine..

My Vostro 430 and Inspiron 5559 refused to go beyond W10 1809. Using advice from the MS and Dell sites, I tried several tricks to resolve issue, to no avail.  On the Vostro 430, I mistakenly missed a command prompt instruction which led the computer to open the restore page. I ended up with a successful upgrade, saving my personal files.

On the Inspiron 5559, the partial restore command failed. I therefore resolved to revert to a full restore.  After about 12 hours, I got a message that xTM files (I forgot the first letter on that sequence) were preventing continuation of the process. I clicked on the prompt to resolve the issue.  The computer then entered a sequence of stop-restart, first on 15-second cycles inching up to 2-minute cycles. It has now been going on for 2 weeks.  To resolve this issue, based on a similar post in the community, I tried pressing F12 while restarting: nothing happens.  Pressing F4 will open the SupportAssist page and enter a hardware scan, giving a clean report card... and then resuming the never-ending loop. On a second run, I pressed F2 to enter BIOS (v. 1.7.0) menu. Under SupportAssist System Resolution, I clicked on SupportAssist OS Recovery: no change.  Under General/Boot Sequence, I see that I can inverse the order of boot sequence between Windows Boot Manager (current) and UEFI ST1000LM024... Should I modify that sequence?  The unit came without recovery discs but with a reference to the MS System Windows Restore tool.

Any advice would be welcome at this time.