I bought Witcher 2 last year when the pre-order first opened, and now I am not able to pre-download it. There are no places on the website where I can download it, any help?

I believe that the download should be found on your game shelf under the "My Account" section of the site, where all your downloads should be.

Have you paid for it yet ? That Pre Order you're referring to was just symbolic, the real pre order started yesterday, but you'll have to pay for your pre order before you can pre download it.

The game isn't listed under My Account... I ordered it in November and I remember seeing the money leaving my account.

You're probably mistaken, paying for the pre order wasn't possible at all untill yesterday.

Then you didn't order it from GOG.

This. If you remember paying for it here on GOG before yesterday, then you remember wrongly.

It should be very easy for you to dig up documentation of the purchase, if it exists. I'm guessing it doesn't.

From the Witcher 2 FAQ:

[i]Do I have to pay for The Witcher 2 immediately when I preorder it on GOG.com?
No! Signing up for a preorder on GOG.com won't cost you a penny. You'll get some cool free stuff, though!

When can I actually pay for the preorder?
The Witcher 2 will be available for pre-purchase on May 10, 2011.

How long will the preorder offer last?
You can preorder the game right up until 9:59 PM GMT on May 16, 2011. For reference, that's 11:59 PM Warsaw time, 10:59 London time, 5:59 PM New York time, or 2:59 PM Los Angeles time.
If you preordered the game, you will have time until May 31st to purchase it and take advantage of the 10% discount.[/i]

TL; DR version: You can preorder until may 16 to get access to the preorder goodies right away but you won't get charged for this. If you do decide to buy the game you have until may 31 to pay and still get the 10% discount if you preordered previously.

GOG has this up on their Twitter:

If you need your CD key, fair price package codes, or free bnus RPG, check out http://www.gog.com/en/page/my_tw2_info/