When I click on the GOG Galaxy icon nothing happens.
If I click on the Might And Magic icon the game starts.
But, when I click on the Sacred Gold nothing happens

There have been a problem after updating GOG Galaxy recently !
I have absolutely no idea if that is related to your problem because you are extremely skinny on the details.

So my advice would be that you download newest version of GOG Galaxy from the link at bottom right of GOG front-page and install that !

If that does not fix your problem the contact GOG support and if you can not be bothered to do that then come back here and post more details and hope that someone else can assist you !