Thank you so much for your kind care.
I put all the points you just posted in my mind and in my notebook to apply whenever this, or the like, happens again.
What I tried today was to Re-install Windows 10, with the option of Keep Documents and Software in place.
The Re-installation process took 5h 20m.
I soon checked my Kaspersky Free's Fast Scan. It took only: 20m, ie the usual time I'm used to; and now i'm about checking the Full Scan time, which should be around 2h 30m.
The 2nd change I mentioned to you yesterday (=the Number of Processors of the CPU, that could be accessed thru msconfig Boot Advanced Options), returned normal after today's re-installation.
I wished to inform your kind self and the Community here of today's results, so that this experience could be exchanged.
Again, thank you, and all who gave me advice, so much for the kind care.
I'll always think of you, and the Community here, as a true support, whenever needed.