Product Key Issue

....I recently purchased a notebook but the issue is that the product key it came with doesnt work...
how can i solve this particular issue..

 

It just might be possible that this notebook had Vista on it, but later had XP installed onto it. The tech doing this job may have just put XP on, and then passed it on to retail, leaving the original Vista license sticker on it. I have a couple of computers at my place of employment in exactly this condition, even so far as to have the shortcut in the Start Menu to create a Recovery DVD for Vista.
As Steve has suggested, you need to contact the seller.