After failing to log into XFCE ...I tried a different display manager to lightdm (I installed Slim to no avail).
I tried creating a new user account - that did not work.I also checked the permissions of .Xauthority and various other files - no use.
The only thing that worked was...I used Ctl-Alt-F1 to get a normal terminal, and then installed LXDE (apt install task-lxde-desktop). After rebooting I was able to log into LXDE without any problem.
