Home and Pro are two separate downloads. You had no choice but to install Home if that's what you downloaded. You could have downloaded Pro and clean installed it on the PC that came with 8.1 Pro. Whether your installs stay activated, only time will tell? All I can tell you is if I download install 8.1 Core from here, http://windows.microsoft.com/en-us/w...-refresh-media it will use my laptops 8.0 embedded key automatically and activates online automatically. If I download 8.1 Pro and try to install it on that same laptop, it rejects the key and prompts for one. I have to enter a Pro key to continue the install. If Windows 10 does the same thing, your 8.1 Pro key should have been refused when you installed 10 Home. It wasn't, which leads me to believe it doesn't look for Windows 8 keys. Just an observation mind you. Also, OEM Windows 7 PC's with no OS installed, will have no key to find. It's not embedded in the BIOS for Windows 7. No way to determine what version of Windows 7 was installed either to figure out what version to install as part of the free upgrade.