John is having issues with Windows 8.1 and a hard drive failure that has wiped out his Windows key. Leo says if he doesn't have the key, he'll have to contact Microsoft. There may be a way to recover the key from the hard drive. The chatroom says Belarc Advisor can give him the key as it will have it listed in it's register. Leo says that Microsoft also saves the product key in his Microsoft account, so he can log in with another machine and see it. But John says that Microsoft has blocked the key, so it won't help. Leo says the boot UFEI firmware saves it as well. So he could do a restore and the firmware should take care of entering it. But if Microsoft has blocked it, then he'll need to contact them to get a new key.
John should try one of these links: