  fireberd - I have made progress on this issue, but not from a direct approach. It seems that the solution to my OTHER issue, about F1 - F12 keys not working unless one also held the Fn key, has helped here as well.  See [URL]#M62303  To solve the other issue, I typed Fn+Esc to go into "Fn Lock".  Since then, sitting at the keyboard (our new wireless keyboards), the constant top-center display warnings about Num Lock Off and On (whenever I hit Shift+something or Win+something) have stopped. However, if I remote in to the same PC using AnyDesk, the problem continues.  But as that is only me and represents 0.1% of the use of the PC, I'll live with it.  At least it won't torture our employees. I scoured Settings to look for anything related and didn't find anything that changes the outcome.  My cursory review of the new BIOS didn't find anything either, but I would need to check that again to be confident. Once again, Dell has done something "extra" that is entirely non-ergonomic with little concern for its small business customer who puts in a lot of work without in-house advanced IT help to make things run well.  If Dell is going to inflict top-center screen warnings about something (when these warnings are not Windows standard), Dell should provide an option to turn them off.  In this case, that option does not exist. Very frustrated, and we spent approx. $6,000 on three new PCs. And since I don't know what actually helped with the issue, there is a risk it will recur.  Please watch this space.  
Just got three new Dell PCs - one Precision 3660 Tower and two Optiplex 7000 Towers. Per my orders, all three came with the Dell wireless keyboard and mouse model KM5221W (the box label says KM5221WBKB-US). On at least two of the PCs and maybe all three, the NUM Lock goes on and off by itself in response to unrelated keystroke combinations.  A lot. For example, CTRL + SHIFT + Esc open Task Manager (correct) but also causes NUM Lock to toggle On or Off (wrong).  And many others. How to fix? Could it be related to this wireless keyboard?  See also my different question at [URL]  Thanks.
NUM Lock goes on and off by itself in response to unrelated keystrokes