Failed sign in

Since you didn't specify your account type, I will provide solution based on the tag of the initial post. If you're using a personal account (@hotmai, gmail, outlook.com...) instead of a business account (@onmicrosoft.com, @yourschool.com....), please let me know so that I can provide guidance with more accuracy.

Hi @Alsaei, Aishah a m kh m e alsaei (Student),

Thank you for posting your question in the Microsoft Q&A forum.   

I understand how inconvenient it must be to encounter error 500121 and be unable to access your account. 

The error code 500121 generally indicates that the sign-in attempt was blocked due to a failure in meeting Multi-Factor Authentication (MFA) requirements or other security conditions enforced by your organization’s policies. 

Since you are a student in your school, your account is under management of your school's IT admin. You may consider contacting your IT administrator to confirm whether your account is blocked or to follow the steps outlined below. 

You can share this information with your IT administrator for their reference: 

Method 1: Check block sign-in via Microsoft 365 admin center 

Go to Microsoft 365 admin center > Users > Active user > Locate your account and if it’s blocked, select Unblock sign-in to restore access. 

Method 2: Reset Multi-Factor Authentication (MFA) for a user 

Go to Microsoft 365 admin center > Show all > Identity. 

Navigate to Users > All Users, then search for the user. 

Click on the user’s name. 

Under Authentication methods, first select Revoke MFA sessions to reset the current sessions. 

Then choose Require re-register MFA so the user will be prompted to set up MFA again at their next sign-in. 

Method 3: Disable and enable Security Defaults 

In the Microsoft Entra Admin Center > Overview > Properties. 

Scroll down to Manage Security Defaults. 

Click Disable and confirm your choice. 

Ensure you click Save to apply the new settings. 

After saving, re-enable Security Defaults. 

Additional information is available in the following resources: 

Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID |… 

Configure Security Defaults for Microsoft Entra ID - Microsoft Entra | Microsoft Learn 

As community moderators, we kindly ask for your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into performing deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.  

I hope this information is helpful. Please follow these steps and let me know if it works for you. If not, we can work together to resolve this.    

Thank you for your patience and understanding. If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you. 

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread. 

The error code 500121 indicates that the user didn't complete the Multi-Factor Authentication (MFA) prompt. This error often appears if the user hasn't completed setting up MFA. To resolve this issue, you should instruct the user to complete the MFA setup process and then attempt to sign in again.

If the issue persists after completing the MFA setup, further troubleshooting may be necessary, or you may need to open a support request for assistance.

References:

• How to troubleshoot Microsoft Entra sign-in errors