Lucky you.
A laptop's disk failed and I tried that with a new disk and the product code on the bottom of the laptop.
The code was accepted, it installed, and on first reboot a Microsoft Dos screen appeared telling me the code was invalid.
Samsung claimed it was MS fault. MS claimed it was Samsung's fault, despite it being an MS "shan't" message.
Resolution was to buy a third disk with XP preinstalled, for the price of the OS, or to install a linux. Guess which happened.
Later MS refused to sell me Win7, so clearly they don't want my custom.