I don't know that any of these ideas will help, it's just what I looked at when I tried to see what the problem might be.
When you first start the Boards Manager, do you see the message "Downloading platforms index..."? It gets the small file http://www.energia.nu/pacakges/package_index.json . If you can see that, then it's talking to the package server OK. I've got a slow dial-up connection, so it sits there long enough for me to read it (and wait a little, too!). If you have a fast connection then it might blip past in an instant.
It's interesting that it wants to get a 1.0.2 rel