Context

• Suddenly Microsoft Teams Windows client stopped connecting and shows a white page instead or logging in.
• Quitting or rebooting teams did not solve the issue. NO ADFS is in place
• Azure AD Connect is in place with Seamless Single Sign-on enabled

Resolution

Seems that Teams modern authentication is linked to internet explorer settings. IE Settings had javascript blocked because office.com wouldn’t load. This was following a computer setting change. I had to reset the IE settings to fix OFFICE.COM not loading.

After this Microsoft TEAMS was loading !

Error in Microsoft teams logs

Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- event -- Microsoft_ADAL_api_id: 176, Microsoft_ADAL_correlationId: cddc6b2a-fc0d-4b35-925b-4cf14864a0bb, Microsoft_ADAL_response_rtime: 1543103, Microsoft_ADAL_api_error_code: 4c7,Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- info -- Could not login user - status: 4c7 diag:1Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- error -- SSO: ssoerr - (Login Window) Could not login user - status: 4c7Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- error -- SSO: ssoerr - SSO Uber catchFri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- info -- L’authentification moderne a échoué, mais vous pourrez toujours vous connecter. Le code de votre statut est 4c7. diag:0Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- info -- adalsso:statusChanged to: L’authentification moderne a échoué, mais vous pourrez toujours vous connecter. Le code de votre statut est 4c7.Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- info -- Sso failed, updating cookie settings. Status:4c7 diag:1Fri Nov 09 2018 15:00:11 GMT+0100 (Paris, Madrid) <10264> -- info -- Focusing main window

More information about Microsoft Teams modern authentication

Source 

What is modern authentication?

Microsoft Teams has implemented a better way of signing in—we call it modern authentication. (If you’ve ever heard the term “single sign-on ” or “SSO”, that’s what we’re talking about here.) The benefit of modern authentication is that it makes it possible for you to sign in to Microsoft Teams without re-entering your email and password every time you want to start a new session. It’s a more secure and reliable way to sign in to Microsoft Teams.

Modern authentication is a process that allows you to sign in to an app securely. Since modern authentication includes SSO, it’s also part of the process that lets Microsoft Teams know that you’ve already entered your credentials (like your work email and password) elsewhere, and you shouldn’t be required to enter them again to launch the app.

Signing in with modern authentication will vary depending on a couple things, like if you’re working in Windows or on a Mac. It will also vary depending on whether your company has enabled single-factor authorization or multi-factor authorization (multi-factor authentication usually involves verifying your credentials via your phone, by providing a unique code or entering a PIN number or presenting your thumbprint). Either way, once you complete the sign in process using modern authentication, you won’t be required to provide your credentials again—from that point on, Microsoft Teams will automatically sign in to your account once you launch the app from the same machine.