I've tried Uninstalling, reinstalling, running a registry check and fixer, running with Administrator mode, as well as using XP and Win 8 compatibility modes, but every time I start GOG Galaxy the Window opens as a completely white slate, and regardless of time nothing happens. How do I fix this?

I've attached a screenshot.

What is the install location of Galaxy? Could you try starting the client with your antivirus/firewall off? Perhaps some security software interfere?
You may also try uninstalling Galaxy and cleaning things up in case some files are corrupted.
Otherwise contact GOG Support

Fixed.

For future generations the "how" might be interesting...

Post #3 is hilarious. The part about activation reveals the post was written by someone who does not buy games here, possibly a bot.

Definitely. Bot or shill. In any case, reported as spam. Someday I'll find one on a back alley and will teach him manners.

How?