Why is my Windows not activating?

[Windows Central Question]

Why is my windows not activating?

I had upgraded my windows 8.1 to 10. But after a month or so I had to format my PC. The engineer installed 8.1 again with the same serial key. But now my windows 8.1 is not getting activated. Is this because I used 10 for more than a month and now I can't go back to 8.1?

 

[gpobernardo]

Re: Why is my windows not activating?

If you're confident that the license key your engineer used is valid, then you may call (or ask him to call) Microsoft for customer support or for activation via phone number (through Skype). I was able to successfully activate my Windows 8.1 license via this method.

If the license is not valid, then you need to acquire/purchase a valid one.

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