Will i ever be able to download my copy of the game? I had it with my video card and never been able to download it...

What is the problem?

You got a key for Witcher 3 from your graphic card. You had to go to the website of NVIDEA to get a GOG Key. I hope you did this because I heared the promo code expired some time ago. Now redeem the key on GOG (http://www.gog.com/redeem).
Now you have 3 ways to download the game:

1. Use your browser (e.g. Firefox,...):
a) Go to Account - Library - Witcher 3.
b) On the "pop up" go to the left side and click on all 7 parts of the game to download them (1 exe-file and 6 bin-files).
c) After you download them all double click the exe-file to install the game.
d) Do the same for the latest patch (2 parts, 1 exe-file and 1 bin-file).

2. Use the GOG Downloader to downlaod the game. The download links can be found behind the more button on the game "pop-up".

3. Use GOG Galaxy to download and install the game.