I just had a quick question I needed to ask. I'm looking to build a system soon and I need to install an OS on it obviously. I don't really mind Windows 8 and looking at the price of it now, it's about one hundred dollars. However, the upgrade version is only forty. I was wondering if I can use the serial number from another (very old) desktop I have and use it as the base to upgrade to Windows 8? I'm not sure if I would have to move the hard drive from the old desktop to the new one, and that's why I'm posting today. And even if it is possible, is there somewhere I can look to find the code if it was a desktop bought from a store?