Well I was thinking about playing The Witcher Enchanced Edition once again but since my cd player doesn't work I looked for another way to play it, and on the back of the manual inside the box of the game there is a key which is supposed to work on gog, so i go to redeem it on gog witcher backup link but then once i've entered the key it says "This code doesn't look like one of ours. Please check that you entered the code correctly."
My key looks like this: XXXXXXXX-XXXXX-XXXXX-XXXXX-XXXXX
Can anyone help me?

You must contact the support staff.

that's what I wanted to do but you have to go through a few steps and then in function of your problem they ask you the ORDER ID of the product but since i've bought it at a retail shop I don't have it.
So I really don't know where to go.

If the product key is not recognised by GOG your purchase is probably counterfeit or stolen. Which means you have to go back to the store or purveyor you brought it from and ask them for a refund.