I purchased my Dell Optiplex 745 P.C from a Business called Regency Technologies that specializes in buying returned electronic devices, and then testing for resale. I believe they might have stuck a windows os dell tag on the device that is not the original number that came with it. I have the service tag for the device and it is indeed the correct tag, I was wandering if I could retrieve the correct windows product key by using the service tag from the dell manufacturer.