FINALLY SUCCESSFUL...BUT...
An update:
Contacted HP and they indicated that absolutely they didn't support the printer I have, HP Laserjet 4250. The "technical representative" did however spend 15 minutes trying to convince me to buy a new printer, which they would offer a "good deal" .
#1 My printer functions excellently with drivers. #2 What they were offering was substantially higher than Amazon. #3 The printer they were offering is an older model that they likely will soon stop supporting.
I finally was able to install 3rd party software from Gutenprint site. http://gimp-print.sourceforge.net/MacOSX.php
Then it's a bit tricky as you have to disable in Terminal a safety setting temporarily.
Instructions:
1) (re)start in recovery mode (hold cmd-r while booting or hold option and choose recovery volume)
2) start terminal from menu and disable rootless with command “csrutil disable” . there will be some feedback confirming you disabled this safety feature.
3) reboot normally
4) do not double-click your installer but go in package content (right click > view package content)
5) find inside the package Contents>Packages>Gutenprint 5.pkg and use that package to install (double click it). This time install should go normally.
6) I suppose you would like to enable rootless again since it is a safety feature after all with 1) to 3) using “csrutil enable” this time
This worked and my printer and computer are pals again!!!!!!
Thanks very much for all suggestions!!!!