A friend of mine is about to dispose a laptop but asked to have it instead to do some things with it. The laptop is having an activation issue with Windows showing that it's not activated. My friend have limited knowledge about computers, and when it was not booting up, he asked another person and had the OS reinstalled. It's now having activation issue, I'm thinking that it's not the correct operating system installed in the computer.

So I just wanted to ask if there's any way that I can know what operating system has been purchased with the system. I tried to look for any windows sticker and cannot find any.