Cannot connect to myec2 through ssh suddenly fronm today

Hello.

It may be that sshd was not able to start properly.
I think it would be a good idea to follow the steps in the document below to check the system log and see if any errors have occurred.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/troubleshoot-unreachable-instance.html#instance-console-console-output

You may also try connecting to the OS using a serial console or Systems Manager Session Manager.
Once you are able to connect using the serial console or Systems Manager Session Manager, check the SSH logs and status to see if any problems have occurred.
https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager.html
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/connect-to-serial-console.html

Ensure you're using the current, correct IP address - when the EC2 was started today after being stopped yesterday, it would have been allocated a new & different public IP address.