Let’s say that you have lost the sticker with your Windows serial key and you want to re-install your operating system.
No need to worry, you can still find your serial key as long as your operating system is still running (not damaged beyond repair).
So click on “Start”, in the search bar write “regedit”.
From there go like this: HKEY_LOCAL_MACHINE > Software > Microsoft > Windows > Current Version. You will see “Productld”. Right click on it, click on “modify”.
Your current serial number will be displayed there.
Note it on a paper and you are good to install a fresh copy of Windows.