I\'ve just started working with Cassandra (datastax), version 2.1.3 and cqlsh version 5.0.1.
Cassandra starts up fine and the cluster is operational instantly.
try changing the native_transport_protocol to port 9160 (if it is set to anything other than 9160; it might be pointing to 9042). Check your logs and see on which port cassandra is listening for CQL clients?
native_transport_protocol
9160
9042