Hello Alicja,
Thank you for reaching out to Microsoft Q&A Support forum.
I can understand you have a valid Office 2016 product key, but after installing it on my new computer, activation fails. I can relate the inconveniences this may have caused, not to worry, I am here to help.
This usually happens when:
The product key was never linked to a Microsoft account, or
Office is trying to activate using a different method than your license supports (e.g., expecting a Microsoft 365 subscription instead of a standalone license).
Steps to Transfer and Activate Your Office 2016 License
Let’s try the most reliable method to activate your perpetual license:
. Check if Your Key Is Linked to a Microsoft Account
Go to https://account.microsoft.com/services/ and sign in.
Look for Office 2016 listed under your products.
If it’s there, you can download and activate Office from this page.
If it’s not listed, your key might not be linked to your account, and you’ll need to activate it manually.
Kindly check this link to see how to resolve activation issues:
https://support.microsoft.com/office/fixes-or-workarounds-for-recent-office-installation-or-activation-issues-30453145-72e9-4061-a88c-cd74884f292f
Also, this link provides information about Office 2016.
https://support.microsoft.com/office/end-of-support-for-office-2016-and-office-2019-818c68bc-d5e5-47e5-b52f-ddf636cf8e16
If the issue persists, I suggest you contact Microsoft live support in order to further assist:
Here is the link: https://support.microsoft.com/home/contact
Type this keyword and press Enter: Contact Support.
At the bottom, click "Sign in to contact support" and sign in with your personal Microsoft account, or click "Contact Support" if you're already signed in.
In Product and services, select "Microsoft 365 and Office".
In Category, select "Select **“**Activate my product” or “Product activation”
Click "Chat with a support agent in your web browser".
I hope these suggestions helps!
Thank you for your time.
Best Regards,
Obyziotta / Microsoft Q&A Support Moderator