windows xp or vista

It is not pirated I have a valid key that allows me to download the software but since I bought the product used when I try to register it microsoft says it been registerd to many times so they say basically im screwd. My copy is the original CD's and key code yet that doesnt matter to microsoft so now im looking for the alternative way to use it such as a different key?
THANK YOU

 

Well did you try calling microsoft ?.......takes a while to get through but i had simalar problem with my microsoft office and i got a costomer service rep and they basicly gave me a new key ( they were probly fed up with me by then but anyhow ) i got a key that worked

 

thanks I will try them again

 

Windows ME