Office 2021 not working, says my license isn't activated

End of support does not cancel a perpetual Office 2021 license; first verify that Office 2021 appears under the Microsoft account that originally redeemed it, then repair activation using the matching Windows or Mac steps below.

1. Verify the account that owns Office 2021

1. Close all Office applications.
2. Open Services & subscriptions and sign in with the Microsoft account used when Office 2021 was purchased or redeemed.
3. Confirm that Office 2021 is listed.
4. Open Word and sign in with that same account.

After a product key has been redeemed, activation uses its associated Microsoft account; repeatedly entering the key can produce an “already used” message without meaning that the license is invalid.^1^

If Office 2021 is absent, try any other personal Microsoft accounts that could have been used for the original purchase and search old email accounts for the purchase confirmation. Microsoft’s activation guidance states that an account without the Office product attached cannot activate it.^2^

2. If this is Windows

Since Refresh/Update License already returned error 16, do not keep repeating it.

1. In Word, select the account/profile at the upper-right and sign out of Office.
2. Close every Office application.
3. Select Start → Power → Restart. Use Restart rather than Shut down.
4. Open Word and sign in with the account that owns Office 2021.

If activation still fails:

1. Open Control Panel → Programs → Programs and Features.
2. Search for Office.
3. If multiple Office installations appear, uninstall only the version you no longer use, restart Windows, and test Office 2021 again.
4. If only one installation remains, select it and run Online Repair, then sign in again.

Multiple Office installations can conflict with activation, and Microsoft recommends Online Repair when removing the extra installation does not resolve it.^2^

Also verify Settings → Time & language → Date & time → Set time automatically and Set time zone automatically. Incorrect system time can prevent activation.^2^

3. If this is a Mac

Error 16 is reported primarily in the Mac activation flow. Reset the stored Office activation credential:

1. Quit all Office applications.
2. Open Spotlight, search for Keychain Access, and open it.
3. Search for Office.
4. Delete the Office data-license credential.
5. Reopen Word and sign in with the Microsoft account that owns Office 2021.

Microsoft documents this credential reset for Office 2021 for Mac activation failures.^3^

If Office confirms the purchase but still cannot activate:

1. In Finder, select Go → Computer → Macintosh HD → Library.
2. Locate PrivilegedHelperTools.
3. If the folder has a red stop icon, correct its permissions; if it is accessible but empty, uninstall and reinstall Office, then activate again. Microsoft identifies access to this folder as necessary for one-time-purchase activation.^3^
4. Check Microsoft’s current Mac activation-issue list before reinstalling, because an activation failure can also be an emerging service or product issue.^4^

If reinstalling becomes necessary, download Office from the account’s Services & subscriptions page rather than redeeming the product key again. On first launch, open Word, select Get Started, and sign in to activate.^5^

If the license is listed but none of these steps works

Contact Microsoft Support while signed into the account that displays Office 2021. Provide:

• The exact edition, such as Home & Student 2021 or Home & Business 2021
• Windows or macOS version
• Screenshot of “License: Not Activated”
• Exact error text and code 16
• Purchase receipt, but not the full product key in a public post

End of support means no further security updates or technical support; it does not itself revoke the installed license. Microsoft explicitly states that organizations can continue using Office LTSC 2021 after support ends, although doing so carries security and reliability risks.^6^

References

1. "This product key has already been used" error in Office
2. Unlicensed Product and activation errors in Office | Microsoft Support
3. What to try if you can't install or activate Office for Mac
4. Fixes or workarounds for recent Office installation or activation ...
5. Office for Mac 2021
6. October 2026 announcements