Click play through Galaxy client button greys out nothing happens then goes green. Click on the icon from the start menu nothing happens. It will launch if downloaded and installed manually.

Try reinstalling Galaxy.

Greetings.

I had the same thing happen to me on Windows 10 Professional.
Try installing XNA. You can find the setup executable of it in the "__redist" sub-directory in your Sots-Gold-Edition folder.
That's what did it for me. Hope it works for you too.

I just checked, to see what would happen if I tried to start SotS:TP on the Galaxy client.
I'm using Windows 10 (Pro), 64 bits.
It worked just fine here, with the latest version (Galaxy v.1.2.5 beta).
It loaded the game (the main menu, the 'Message of the day' window), and I loaded an old character. Everything is in order.

Reinstalling Galaxy didn't help, OP? Have you selected the game and clicked at Verify/Repair option, in the client interface?
To see it, you have to first click at the gray 'MORE' button (which is to the right of the green 'PLAY' button), then move your mouse cursor over 'Manage installation', many options will apear, click in the option to repair SotS.
Have you also tried uninstalling SotS, then updating the client, and after that installing SotS with the client? Maybe the problem occurred when Galaxy was importing the game's folder.

Have you followed SnuggleRays' advice?

I presume you've already sent a message to g0g support, but if that somehow didn't happen yet, click here to open your ticket.
And be sure to check your junk/spam folder, sometimes the email service likes to throw perfectly fine emails 'away'.