August 2017
I recently wanted to play some Mass Effect, which I haven't actually finished. So I found my CD (I got my copy from CD-Action magazine) and installed it... but I couldn't load my old savefiles, because, supposedly, I didn't have Bring Down the Sky installed (which, I believe, was part of Extended Edition, or however you'd translate "Edycja Rozszerzona", I had). I quickly found a thread with DLC codes for "classic Origin games" (https://help.ea.com/en-us/help/origin/origin/download-dlc-for-classic-origin-games/) and downloaded missing content. But after that, when I tried to launch ME, i got a message (in Polish, which is weird, as I wanted to install it in English) saying, that I need to re-enter my registration key. The problem is, that no matter how I'd enter the key (with "-", with spaces between, in one "word"), the message would reappear, demanding my registration code. Any idea how I could fix it?
August 2017
The easiest way to solve this might be to redeem your CD key in Origin and download a digital copy. (Is your Internet connection good?)
To do so click in the Origin menu at "Origin" > Redeem Product Code.
September 2017 - last edited September 2017
I tried that before writing here, but it said my key has been already used (although I don't have ME on my Origin account)
September 2017
If that is the case, you should contact EA directly. If you are not from the US change the country in the top right corner.
Support could be able to add the game to your account.
If you have trouble with the contact attempt look at this guide.