Signing in to Excel

The prompt to “tap your security key on the reader or insert it into the USB port” indicates that Excel is trying to sign in using a strong authentication method (a hardware security key) that is associated with the account being used. When this method is required or preferred on the account, Office apps can start requesting it even if they did not do so previously.

In home scenarios this can appear suddenly after:

• Changes to the Microsoft account sign-in or security settings.
• A recent subscription renewal or account refresh.
• Cached identity data in Office becoming invalid or corrupted.

To resolve sign-in loops or repeated sign-in prompts in Office on Windows, a common and effective step is to clear the local Office identity cache so that Excel can prompt for credentials again and register correctly:

1. Close all Office apps (Excel, Word, Outlook, etc.).
2. In File Explorer, go to: C:\Users\<YourUserName>\AppData\Local\Microsoft
3. Delete the folders named identitycache and oneauth.
4. Start Excel again and sign in with the Microsoft account associated with the subscription when prompted.

This forces Office to rebuild its local sign-in state and often stops unexpected or incorrect authentication prompts, including prompts for methods that are not actually available on the device.

If the problem persists after clearing the identity cache, contact Microsoft support so they can check the account’s security configuration and remove or adjust any hardware key requirement that does not match the way the account is used.

References:

• How to fix the issue with MS Office asking you to log in every time you open an Office app - Microsoft Q&A
• I have issue signing in to my microsoft office account. - Microsoft Q&A
• My username and password have stopped working
• Microsoft account sign-in helper