i'm sorry to tell you that you are out of luck. TechSpot doesn't support any inappropriate method to get around licensing issues (i.e. simply getting a key via the forums)
Am afraid the only person who could legally help was whoever sold it whether a) they gave you a key or b) you sued them to return your money. Of course, seeing as how you bought this at a swapmeet neither is likely to happen.
Chalk this one up to experience and be sure to get legit licensing keys at the time of sale (or legit re-sale)