Which compiler are you using?
Also, you didn't mention this, but does "mpirun hostname" give the
expected response? I (also new) had a hang similar to what you are
describing due to ompi getting confused as to which of two network
interfaces to use - "mpirun hostname" would hang when started on
certain nodes. This problem was resolved by telling ompi which
network interface to use (I forget the option needed to do this off
the top of my head, but it is in the FAQ somewhere).