Ambari stopped working after I restarted the Ambari services

I installed the Ambari server and ambari agent on my main machine. It is worked first time. I restarted the services then this got stopped.
I got this message from the logs saying that.
04:40:06,777 WARN [Thread-1] HeartbeatMonitor:121 – Heartbeat lost from host <hostname>
I got this messages from all the data nodes. And also got the message like the HBase Region Server process connection refused message from Ambari console.
Can you please give me the clues why heart beats are not working?
How to check these heartbeats from the clusters? What are the possible reasons for failing the heart beats.

Thanks.
Naresh