Hi so yesterday i installed The Witcher 3 and played it for a while.
Today when i try to launch gog galaxy nothing is happening even if GalaxyClient is running in task manager

Any idea how to fix that? Its not working if i try to launch it as admin

And second question
If i reinstall GOG i'll have to download Witcher 3 again?

You shouldn't have to reinstall the game again, but I can't guarantee that.

That aside, you don't need Galaxy to play the game. You can run it just fine if you start it from the executable in the install folder (not the launcher, but the executable itself) - and if you prefer running it that way, you can just make a desktop shortcut for it. Do note though, that you won't get achievements if you don't run it through Galaxy, if that matters to you.

No, there is no need to reinstall any GOG game after reinstalling or even removing GOG Galaxy. You might have to import these games into Galaxy again but the last tiem I tried it Galaxy was automatically importing all installed games it found.