IP address and host name are not working

All out of sudden, I'm not able to access my EC2 via my hostname or IP address, just by amazon public DNS.

Maybe I should make it clear that everything was working smoothly until last 24 hours.

What would have happened to cause this?

I'm not sure. Can you access

I'm not sure. Can you access the admin portal at https://[publicDNS]:3000 ? Have you rebooted the instance?

Sure and I can ssh using the

Sure and I can ssh using the PublicDNS but the host name is not responding, neither the IP.
Everything was working just fine and it did happen out of sudden.