That's not the problem, the entire setup just doesn't start, he shows the little picture with sourceforts 1.9.4 and before i can even pick options or choose the path it crashes
Download the archive version of the game, and extract it into your Steam/steamapps/SourceMod folder.
The installer reads Steam's registry entries to check whether or not Steam is installed, and get the path to your Steam directory. Obviously something is going wrong with the check and it can't find Steam's entries.
Any decent archive program will be able to extract .tar.gz and all you need to do is extract the folder (sourceforts) into your SourceMods directory. Then the game should appear in Steam once you've restarted.