http://www.gog.com/en/support/the_witcher_2 is the GOG download version for support url. Perhaps there is an answer in there somewhere that would help you, even though you have the hard copy so to speak.
http://www.en.thewitcher.com/ is the official forum, with areas that will provide some additional assistance for you. If you still need additional support after searching on your own, there is a contact for CDPR on the website.
I would love to help more, but at the moment, you probably need a pick and a wire brush to excavate the answers you need for yourself. All computer systems have different needs. With both Witcher games it seems that settings can be as individual as each user, so there is generally not just a one answer serves all kind of fix. Good Luck.