I downloaded Gabriel Knight 3 and the first time it booted up without any problems. Then I changed the the 3D driver from the advanced options to my Radeon HD 6870, but that made some of the mouse icons disappear, so I changed it back to the default option. As soon as I did that en error prompt appears saying "Unrecognized fatal exception", and when I press OK the game crashes. I tried to start the game again and it showed the sierra intro, the main menu and the starting screen (the one that tells the time and the picture of the conductor), but as soon as the gameplay starts, the error prompt appears.

After that I searched online for help and downloaded the batch file from the sierra help desk that changes the name of some file so that the game could recognize it, but it didn't work. The site also said that the error prompt could appear if the files on the hard drive had trouble reading some of the files in the CD-ROM, of course this could not be the problem. Then I tried to completely delete any sign that the game was ever on my computer and downloaded it again, but still the error prompt was there.

Now I have no idea what's causing it and no idea how to fix it, so if someone could help me I would be incredibly grateful.

Wit further investigation I realized taht I didn't change the 3D driver the the default one, but to "software renderer". Since you can only change setting while in gameplay, I can't change the driver back to the default one.

So now I need to know how I can change the game settings outside of the game.

If I recall correctly, GK3 had an options file for changing options before you start the game. But I can't remembver if that's the original or the GoG-version, check your gamefolder to se if you find anything similar.

If not, you have to reinstall the game, just keep all savegames and you'll be able to pick up from where the shit hit the fan.

I'd like to point out that I am completely unable to play this game, unless I can resolve this problem somehow.

Well I found the solution:

I launched the registry editor and from there I opened the Sierra On-Line file and deleted the Gabriel Knight 3 file (from there you could've changed some of the setting, but I found it easier to just delete the damn thing), reinstalled the game and the problem was solved.