If you are running Ganglia in a non multicast environment, it may be the case where a gmond process occupies 100% of the system’s CPU. In such cases it is helpful to check whether the node should be deaf or not (when it is a node that should not receive any messages from others). So try to set in your gmond.conf:
deaf = yes
and see what happens. This has happened to me on CentOS 6.x systems.