If you see the "Activation Failed" error message, it means that your product key is not valid. There are a few things you can do to fix this:
1. Make sure you're using the correct product key. If you're not sure what your product key is, you can find it in the Order History section of your Microsoft account.
2. If you're sure you're using the correct product key, try entering it again. Make sure that you're not accidentally adding a space before or after the key.
3. If you're still having trouble, you can try contacting Microsoft support.