Things you should know:
A Windows 7 or Windows 8/8.1 product keycannot activate Windows 10. Windows 10 uses its own unique product key.
By default, Windows 10 builds are pre-keyed, meaning, you do not have to enter a product key and should not be prompted to enter one as long as you upgraded from an activated Windows 7 or Windows 8 or Windows 8.1 license or Windows 10 Preview build.
If you perform a clean install on first attempt, you will have to start over from an activated Windows 7 or Windows 8/8.1 installation.
If you are prompted to enter a product key, clickDo this laterand give it a few days, Windows 10 will activate automatically.
Activation servers are being overwhelmedat the moment because of the volume of upgrades, so give it some time if you get an error message such as (0XC004E003, ,0x8007000D, 0x8007232b or 0x8007007B) Windows 10 will eventually activate as long as you upgrade using the appropriate method.