Nice, I had the same issue but microsoft refuse to help me. First time called they want me to do clean install from original 8.1 but the old key cant be used anymore. Second time install, they (another guy) straight away they told me to contact my oem provider for a key replacement, which pretty much fuck up if you do the free upgrade like mine from oem. They said we can call them to reactivate back if change motherboard (due to motherboard failure) on a same PC, but looks like it's all bull shit talk.

No more support for them, I will either go pirate or find a cheap key online.