I have a HP 6735s laptop, came with Vista home pre installed. I have now upgraded to Windows 7. My son has a desktop built by myself, so no brand on it. Can I use the serial that was used when installing the vista to my HP laptop as i recovered it using Keyfinder, as i believe that it will come up saying invalid key as it isnt a HP machine. Or do i use the product key that on the sticker on my laptop. Would i need to call microsoft to enable this key? Thanks in advance for your help.