I bought a second hand acer laptop with a legit copy of windows xp pro(stuck to the bottom)I just found out that the copy installed is not genuine,so I rang MS and they informed me that the product key that I have is in fact genuine,but it isnt the same one installed on the laptop.Not sure how and why it was done like that .How do I change the illegal key to the genuine key?I dont have the windows xp pro installation disk....I do but it is really scratched and wont work.Any help would be so fantastic.Thanks