Since your application is accessible for browser, I hope you know how to configure the inbound connections. I believe your machines IP address has changed due to which you are not able to access. Your IP can change if you have reset/switch on/off the Internet or if you are connecting from a different Internet connection after the initial server configuration.
You need to follow these steps
Open the inbond connection for SSH
1. EC2 bashboard - > click the respective Security Group
2. Select the Public SG - > click inbond tab
3. Add an entry SSH | TCP | 22 | Select MyIP
Kind Regards
Robin