So I have a question regarding operating systems. I recently built a new PC and I needed a OS on it, I did not have a optical drive so I decided to plug in my new hard drive (for the recently built pc) into a older pc that had a optical drive. ..I removed the older pc hard drive so the only present hard drive was the new one. . I continued to install windows 8.1 OEM onto the hard drive. . Now when I use my new pc it says my product key is in use by a different pc.. when I'm on my older pc it is using its own OS.... how do I fix this?