My my sincere gratitude for your helpful guidance, well written tutorials, and time and effort for my issues.
I have the DELL Win 8.0 OS on DVD and DELL OEM Driver DVD in hand. I wonder if I would face less risk of loosing my data files with the USB Win10 installation media? DELL calls it an OS Parallel Reinstallation, I think.
I will think on this before going ahead.
Also, does MS provide direct support to my Win10 upgrade issues?
P.S. This mess was most probably caused when I shut off the PC by use of the power switch; the PC was in sleep mode for long while, and I was seeing a totally dark/black monitor screen. May have done damage to area on HDD.