Nirsoft has one application which let you find product and license key for your Windows machine and most other software and games. It doesn't matter if you got a free upgrade or a new key for a clean installation you will need to reenter product key to activate Windows 10 copy again.
Follow these procedure to Find Product key for Windows 10
- Download and install NirSoft ProduKey from this link.
- Now run the program and you can see list of programs with their product key.
- Double click on program to see product key.
This application let you see stored product keys in your hard drive along with all other keys of installed software. In case if you need to recover your Windows bios product key then this software is very helpful.