Data Collector or Data Aggregator are unavailable.
Performance Management 2.7+
The first step to take is to check in on the logs on the specific device. For example on the Data Aggregator you would check the /opt/IMDataCollector/apache-karaf-2.4.3/karaf.log and you may find this line:
ERROR | Manager-thread-4 | 2016-07-19 14:38:07,006 | shutdown | ces.shutdown.ShutdownManagerImpl 131 | ommon.core.services.impl | | Shutting down the data aggregator.It was detected that no data repository nodes were contactable. The uncontactable hosts are:[HOSTNAME]
The above error tells you that the Data Repository is down and with the Data Repository down, the Data Aggregator cannot function. This same pattern also holds true for the Data Collector but the log you check is the /opt/IMDataCollector/apache-karaf-2.4.3/shutdown.log:
2016-05-31 16:00:30,762 | WARN | roxyReg-thread-1 | shutdown | om.ca.im.osgishell.BundleManager 139 | 190 - com.ca.im.data-collection-manager.osgishell - 2.7.0.RELEASE-167 | | Unable to connect to the Data Aggregator at host <HOSTNAME>. Shutting down the Data Collector. This may take up to 10 minutes.
This error tells you that the Data Aggregator is down or you are unable to connect to it. Both of these errors will show if the Data Repository falls as the services are dependent on each other and will cascade down.
You must make sure that the Data Repository is online and functioning then that the Data Aggregator is online and functioning before you can have Data Collectors or CA Performance Center up and running.