Jim,
My neighbour had similar Dell issue that you described. If I remember correctly , it was called "boot loop". Honestly, I forgot how we solved it.
Maybe I am wrong, but I vaguely remember Dell recovery USB flash was involved.

Can you get to "restore point" from diagnostics?

P.S. If you have some data that...you do not want to lose, which you feel you might, maybe a good idea to pull drive out and clone it.