Hi @Aung Thu ,
1.If you simply failed to log in to the Microsoft 365 portal with your account, it is recommended that you try the account recovery option and try logging in InPrivate mode with a new browser. Or you could contact your administrator to confirm if there is an issue with the account license and if the account is still active and not expired.
2.If you are invited to collaborate in a shared SharePoint folder as an external user, you need to verify that your account is added as a guest to Azure Active Directory in your organization's tenant.
Microsoft 365 admin center > Azure Active Directory admin center > Users > All users
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