Thanks for all your help david. I really appreciate it.
ha ha DONE IT! Got it working and downloaded my first book via wifi
As you said, the problem was the firewall settings. In "Allow a program to communicate through Windows Firewall" I did have Calibre in the exceptions list, twice for some reason. But with one allowing Public and the other allowing Private. So I checked/ticked all the 4 Calibre boxes so as to allow both Calibre exceptions in the list to allow both Public and Private. And it worked.
Thanks again david.