Thank you @Fabby
Sorry I forgot to add that, I added a note above:
“My desktop is KDE since the installation of this system”.
I never run two DE in my system, maybe some “tweak or app” installed in the beginning “confuses” the system 
So, the best thing is to back up the current one and leave only the pacnew in its place as you recommend?
I wish I could prevent the worst, but right now I can’t even connect a usb because it doesn’t recognize them until I reboot the system.
Regards
Solved.
After using *sudo pacdiff, I managed to find and get rid of all those old .pacnew files, then I reboot my system and after a few distressing seconds with the black screen this start with the login screen.
And I see that those new lines that refer to gnome appeared for the first time during this or the previous update.
I also found that some previous update, wreaked havoc on the shadow file; no wonder many people have complained that they cannot enter with their passwords, that new “/etc/shadow.pacnew” comes only with the “root” account:
root:*:14871::::::
Regards!