groze: Well, at least you solved part of your problem. As for the rest, I'm afraid I can't help you, as I don't own The Witcher 3. As someone said before, you are better off just taking this discussion to The Witcher 3 subforum, because most, if not all of the people there actually have the game and are more likely to help you with this. You're posting this on the General Forum, and a lot of users here plain and simple don't own Wild Hunt (TW3), so it's harder for us to help you. Plus, we know nothing about your system's specs, maybe your machine simply doesn't meet the minimum requirements in order to run the game? We can't say.
What I'm about to say sounds like I'm a pretentious elitist snob, and I apologize in advance, but I honestly think a lot of new users migrating from Steam don't know how to live without clients anymore, and they think GOG Galaxy is mandatory, like the Steam client. It isn't. You can download, install and launch every GOG game the old fashioned way, like we used to do before digital distribution of games and had to install them from physical media. I understand GOG wants/needs to push Galaxy further, but I sincerely advise every one to wait for Galaxy to leave beta and, then, install it and use it. As it stands now, it tends to create more problems than the ones it was created to solve.
I don't think playing games without using Galaxy involves "programming nerd-like skills". It's actually quite simple: open your internet browser (Mozilla Firefox, Google Chrome, Opera, Safari, heck, even Microsoft's own Internet Explorer -- you know?, the program you use to access the internet on your computer), type 'www.gog.com' in the address bar, log in, click the big 'ACCOUNT' in the top right of the GOG site (next to 'SUPPORT' and 'Search') and that should take you to your GOG Library (your collection of GOG games). From there, look for the game you wish to download (in your case, that would be The Witcher 3: Wild Hunt), click on the game's icon and you should get a drop down menu with links to download the game (which, in Witcher 3's case, I would assume are A LOT of links). Download *everything* to the same location/folder, then run the only *.exe, and install the game. After having installed it, simply run the *.exe of the game, the Start Menu shortcut, or the desktop shortcut. And, voilá!, it's done. Definitely more troublesome than doing it using the client, but at least you get to control more what you're doing and it doesn't suffer from the problems some games are known to suffer when trying to launch and play them using GOG Galaxy.
not offended as i have a pure gaming machine with dual drives..graphics cards 2TB memory and so on :)
first time i had a problem like this though.Think all my experience with STO,lotro and so on gave me patience de grace.That the game runs in the background does confuse me a little.Thinking i may have to uninstall the gog platform and try to run the game without it.It may give me another insight what i have to do.My problem consist of uninstalling the gog WITHOUT uninstalling the game itself (with all its contents as it says) and to have enough coffee to support me through the process