I recently updated from win 7 to win 8.1, and had to re-instal LR. I upgraded to LR 5, and paid on the basis I owned LR3.6, but then could not find my old activation code, which was required. I then bought a Creative Cloud membership, and upon entering my account, found my old purchase details there, including the activation code for LR 3.6. I should have recorded it then and there, but didn't. CC download was OK, I have downloaded PS, and the downloads page tells me I have an up to date version of LR 5 already. But I cannot open it, as it is asking for the old activation code still, apparently still trying to complete the upgrade process. But now the details of that original LR 3.6 transaction have disappeared from my account page, and i am stuck. i have paid for both the LR5 upgrade and the CC subscription, and I STILL don't have the use of Lightroom.
>should have recorded it then and there, but didn't
OK... try Lost serial # http://helpx.adobe.com/x-productkb/global/find-serial-number.html
And create a document (text file works) with all of your information... I have one, and copy it to a USB drive every time I add a new program