as for a quick reply, the method 4 with modded boot.bin RGN file, I believe I didn't do it correctly.
I did not expect the issue could be so complicated and involves a lot of technical stuff. but I will keep on reading.

The thread by Alexander2010 "Nuvi 12xx,13xx,14xx,16xx with "software missing" on first step of flashing process" leads me to think that the issues mentioned by him could be related to mine. Most probably I will order some tools for the operation.

In the meantime, I will try the QuickCure from the cure3 thread and if no luck, I will go for QuickCure with flasher & further.

I shall read and experiment and report by the end of the day.

P/S: Thanks for the clear instruction and links.