SSH connection from my local terminal to EC2 ubuntu instance is timed out.

Hello, I created an EC2 ubuntu instance and connect that instance through SSH from my local command prompt and connection was successfully. After sometime i close my terminal, reopen my local terminal again and try to connect the same instance but this time it gives timed out error. if i create new instance and connect to it it connects successfully. Mean each instance is connected through ssh connection only once. if i close connection and try to reconnect it gives timed out error. I set the security rule to permit SSH connection from anywhere. Can you please help me in this regard thank you.