Thanks for the suggestions.
Did as you suggested and re-entered language and switched from my normal wired Mac extended keyboard to my unused Blue Tooth Mac extended keyboard. Neither change worked.
So problem of inability to enter Admin Password continues when operating in normal mode. Also unable to enter my Admin Password any time it is called for like when trying to conduct ‘computer scan’ in Tech Tool 9.5. Other apps also call for Admin Password and can not input.
Almost afraid to reinstall again High Sierra for fear will be locked out of computer. Have never seen anything on how to recover from lost Admin Password, but mine for sure is not lost. I just can not input the correct one or any letters/numbers etc., are accepted in the spaces.
As for the additional problem of Mail and Finder not opening from the Dock using a single or double click, that mystery also remains. In both cases the when try to open from the dock, the tool bar at the top of the screen remains opaque. Only when I right click and select “New Viewer Window” for Mail and “New Finder Window” for Finder, do they then fully open on the desk top.
For a while after I last reinstalled High Sierra the problem went away, but only for a day or two.
Thanks again. Maybe I need to just solve one problem at a time and look for "Unable to enter correct Admin Password" anyway hoping for the best.