Examples of operating systems: Windows 98, Windows NT, Windows XP, Windows Vista, Windows 7, Windows 8, Ubuntu (Linux), MacOS.
I've once seen a way to open the black command box, I think in Windows XP, in the login screen and you could change passwords with it.
But again, I don't remember specifics. I've just told you this so you might be interested in trying to google for it and solve it for free, rather than getting ripped off by someone retrieving your password for $1000. 