If the account of your Proton Mail has stopped working functioning, there are specific troubleshooting steps you can take to diagnose and fix the issues. The steps are as follows:

Confirm that ProtonMail services are operational by visiting the Proton Service status page. As of the latest updates, all ProtonMail services are reported to be operational.Clear your browser’s cache and cookies, as these can sometimes cause with loading web application.Switch to a different web browser to see if the problem persistsEnsure your internet connection is stable and functioning properly. If you are using the shared network, check if the other users are experiencing similar issues.If you are using a VPN, disable it temporarily and see if it resolves the issue.Always enter the correct email address and password while logging in. If you have forgotten the password, use the password recovery option.If you are using an email client with ProtonMail Bridge, make sure that it is configured correctly. Common issues include port errors and timeouts. Refer to the Proton support page for specific guidance on resolving these issues.

More Info: https://www.resetprotonpassword.com/how-to-reset-my-password-for-protonmail/

If the above steps are not helpful and still the Proton Mail is   not functioning properly then contact Proton Mail customer care for assistance.