I bought a used lappi on ebay, just download windows 10. There's a Microsoft key on the bottom of the laptop, can I use it? Because I don't want to spend money on Windows… And just have no idea about that…
You could download linux mint, it's free and windows looks very similar
It may work.
Windows 7 and 8 keys can be used and upgraded once when reinstalling Win10. You can't judge that from a distance.
In my experience, this works as long as you really install the same Windows. So if the laptop was on Windows 7 and you then reinstall Windows 7 on it, you come in with the same code. If you have upgraded your Win7 to Win10, you can also get into a Win10 with this code. But not with a Win8 code in Win7 or with a Win7 code without an upgrade to Win10.
But it is not Windows
You can install Win10 directly with a key from Win7 / 8 / 8.1 without going through the upgrade path
Of course you can.
