There are rare occasions where some people do get systems that have illegal copies on them and its not their fault, however that being said, you would have to contact microsoft and give them that product id to get a cd key. I would however just recommend you buy a new copy via newegg or some other online retailer.
If you're looking for a free copy of windows or a pirated version don't bring your questions here, as tomshardware does not condone piracy and will not help you.