The Product Key is embedded in the UEFI BIOS. It'll be automatically input by Windows 10 TH2 installation media. If you are asked for a product key however then you have used the wrong Edition of Windows 10 TH2 so should use Windows 10 TH2 Single Language: [URL] Note Microsoft have stated the end date for the free upgrade is in ~3 days so you need to clean install Windows 10 TH2 and activate online before this date.
The hard drive on my customer's Inspiron One 2330 died. Obviously, there will not be a recovery partition on the new HDD that I've installed. Since the Microsoft Windows 8 activation key is embedded in the BIOS, how will I be able to activate the OS if I install from a DVD if there is no recovery logic to tell the install routine where to find the key? Thanks! 
How to reinstall on new hard drive