Note: I did never connect any Microsoft account! I skipped all input dialogs for the product key, connected to my WLAN and it did not activate properly.
#Windows 10 pro insider preview product key install
Windows 10 clean install (formatted the hard drive before) did not work at all! I think the important part is that you have either had the 10240 build installed by upgrading so that your Windows 7 or 8 key is updated to a Windows 10 before you do a clean install. So I have successfully installed a clean version of Windows 10 Pro using the ISO images and it activated successfully. I never had to enter a key so it looks like once you log in it uses the key that’s in the BIOS and automatically activates it. During installation it wouldn’t take the key but once you log in with your Microsoft ID and have internet connection it will take the key that is in the BIOS and activate it. So it looks like if you had the 10240 insider preview build installed it upgrades your key automatically. The computer rebooted and I logged in with my outlook email and checked the activation status and it said it was activated. It asked one more time at the end of the installation and I skipped it again. I had my Windows 8.1 key for my Surface Pro 3 and tried to use that but it wouldn't take it. It went through the normal clean install steps but then asked for a key. I copied the files to a USB drive and booted to it. This is my secondary computer so I decided to take a chance and do a clean install with the ISO images they provided today. I wasn't sure if there was an official update that would be installed or if I already had the latest with 10240 and there wouldn’t be a major update. I have had a Surface Pro 3 with Windows Insider preview 10240 installed on it. I just did a clean install from the ISO images.