I'm using GOG Galaxy 1.2.59.21, and Stellaris won't launch from the interface. The Play button will turn gray, then back to green a couple of seconds later.
However, I can play the game from Windows Explorer by opening stellaris.exe.

My game computer is Windows 7.

Any ideas?
Thanks!

which play button... the galaxy one or the stellaris ui one?
what ticks have you got in the galaxy ui for stellaris?

any ideas = yes Windows 7 is finished unless you have the lastest patch... and even then it gets you til January 14, 2020

Thanks for responding.
I couldn't launch the game from Galaxy. But I could run the game by running stellaris.exe.

I found the following steps that helped troubleshoot Paradox's launcher:

Go to the folder where Stellaris.exe is, and find the file launcher-installer-windows.msi .
Please right-click on that .msi file and choose Troubleshoot Compatibility. Hit Start the Program, Cancel, Yes, Finish, Next. Save the changes that process suggests, then Close. Now manually run that .msi by double-clicking on it and run through the install; if it wants to remove the launcher do that, then run it again to install it.

Reinstalling Paradox's launcher fixed the problem of launching from Galaxy.