Actually, you need to buy a retail license for your Windows.
Be careful, however, because some sellers sell Volume licenses, which are mainly used by large companies, to ordinary users. They claim that they sell in a low price, but this type of licenses may cause issues at a later stage. In other words, they are not legal for ordinary users. So, if you don't buy from Microsoft directly, make sure that the license you are getting is Retail.
When you activate your Windows with a genuine license, we can continue cleaning the computer, if you wish.