I bought a physical copy of the game and I started to play it just this morning. Now it is downlading an update but it doesn't really start the download and I'm unable to play. I tried also to "Clear the download" but the PLAY button still doesen't work. How can I solve? It's frustrating

You could try and leave it to do that downlaod thing. It IS rather useful, since quiet a lot of bugs get fixed this way. Or you could use gog to download a clean version of the game and reinstall OR you simply play without gog completely. You'll find the .exe-file for the game itself in the folder you installed your game into.