Thank you very much, Pat, for your great help. The link has inspired me to download the trial version from the Adobe website and go from there:
"Adobe Download Assistant" was automatically downloaded before the download of the trial version began. With the "Adobe Download Assistant" up and running, the download of the trial version took within 30 minutes. I then got to enter the serial code of my already purchased PSE 12 right after installation of the trial version and completed the whole set-up process (without even opening or using the trial version at all).
It is rather counter-intuitive that one should start with a trial download even when he has gone straight into buying the product. It was as if the trial version was a bridge to facilitate the official download because the trial version provided the "Adobe Download Assistant". Maybe, it is expected that people would always take a trial before buying? Or maybe, it is expected that most people would already have the "Adobe Download Assistant" handy?
Anyway, I am glad there is a solution. In this case, I think the key is to get the "Adobe Download Assistant" which comes with the trial version. Hope this post will help others who might face the same issue too.
Many thanks again.