Hey I knew your problem. Because I saw it on my computer, too. If you willnot solve it, I sure that it will keep appear when you do anything on that computer.
But I dont think that a key you found on internet will help you since people use it one more time, and it's expired in short time.
So I think you can use another way, like a kms for activing your win 10.
Just down it and install and following guide steps. And you will not be disturbed by that messages.