SOLVED!!!
After many (far too many) hours spent by searching for all sorts of possible solutions for my trouble with your (only your) website, it suddenly dawned on me that perhaps you, after all, offered the right solution but not the right way to get there. Namely, the suggested path through "Accessories" and "Notepad" didn't work at all. Not for me.
So I took the "classical" route:
My Computer > C:\ > WINDOWS > system 32 > drivers > etc
And – surprise, surprise! – there was yet another "hosts" file (apart from the one that I had created/modified under your instruction). It had only two entries referring to your website (not five as in the other "hosts" file).
I opened the file with Notepad, deleted both "wrong" entries, saved the file, rebooted the computer — and, here we are: IT WORKS AGAIN!
I described my "inventive" procedure in order to help some other miserable soul like me who would not be successful by strictly following your instructions.
Thanks for all your help and patience. I am almost happy now.