There are lots of ways and at the moment you are vulnerable to falling for all the suggestions most people will make. I suggest you don't do that and follow Hawkeye's advice to but a proper copy. Nothing less will correct this situation so ignore all the offers of "legit" Product Keys.
If you want a free Operating System, look for Linux systems. Many of them cost nothing and need no activation. They do everything Windows can and in many ways, better. You may not be able to play some games but there are equivalents available.