MS Office 2016 cannot sign in.

Dear TC,

When this sign-in window appears, please note that Microsoft offers two account types:

• Personal account: A personal Microsoft account. It may use a Microsoft email domain such as @outlook.com, @hotmail.com, or @live.com. A third-party email address can also be registered as a personal Microsoft account.
• Work or school account: An account created and managed by your organization or educational institution. It normally uses the organization’s domain, such as <yourname>@company.com or <yourname>@school.edu, and may sometimes use an @yourorganization.onmicrosoft.com address.

Please confirm where the account was originally obtained:

• Was the account created personally when purchasing or setting up Microsoft Office?
• Was the account provided by an employer, school, reseller, or IT administrator?

I also recommend signing in to the corresponding Microsoft account | Sign In or Create Your Account Today – Microsoft using the same email address. This will help confirm whether the account is valid, which account type it belongs to, and whether the credentials are working correctly.

After confirming the account type, please return to Office 2016, select Personal account or Work or school account as appropriate, and then sign in with the account associated with the Office license.

I hope the information shared helps point you in the right direction. Please try the steps above and let me know if they work. If not, we can continue working together to narrow this down.

The first response may not always resolve the issue right away, but with your help and more details, we can work toward a solution.

If the answer is helpful, please click "Yes" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 

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