You are talking about serial number when you say "license key". Right? Assuming that to be the case...
All you should have to do is install Premiere Elements 12 from your installation disc using your purchased serial number on your Windows 8.1 64 bit computer.
How many computers now have Premiere Elements 12 with the same purchased activated serial number? If only the Windows 7 64 bit, then you can leave
it there. When and if you have to get Premiere Elements 12 off Windows 7 64 bit, then remember to deactivate (Help Menu/Sign Out) in an opened project before you uninstall the program in the Control Panel.
But if you already have that purchased activated serial number on two computers, then you will have to deactivate the program from one of those two in order to install on the third computer.
All should go well. Do not forget to update 12 to 12.1 Update once you have installed version 12 on Windows 8.1 64 bit.
Please let us know the outcome.
I am not sure what you were involved with regarding the Premiere Elements 12 Windows 7 install, maybe redemption codes, product codes, maybe even what you need in the final analysis the serial number.
But, if you have been using the program on Windows 7, Adobe should have a record of your serial number listed with at the Adobe web site under "My Products". So even if you started out with the redemption code and product code business, I would like that you would be free of that now?
a. If you need Redemption Code, Product Code, Serial Number re: Student Teacher Edition
b. Redemption code in general
c. If you want to check out Adobe for your serial number....Adobe web site http://www.adobe.com, sign in with your Adobe ID and Password, type in
My Products in Search field, and then navigate to your products where you click on Adobe Premiere Elements 12 to reveal your serial number.