Why I can't start graphical interface(gui) on IBM Flex System p460 Compute Nodes ?

Issue

• Complete installation of RHEL6 was performed on IBM Power 7895-42X(p460) Compute node.
• All necessary Packages are installed on the system. But while trying to start system in gui mode using
  startx command, getting error as below:

$ startx
Loading extension GLX
(EE)
Fatal server error:
(EE) no screens found(EE)
(EE) Please consult the Red Hat, Inc. support at https://www.redhat.com/apps/support/ for help.
(EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
(EE)
(EE) Server terminated with error (1). Closing log file.
giving up.
xinit:  Connection refused (errno 111):  unable to connect to X server
xinit:  No such process (errno 3):  Server error.
Couldn't get a file descriptor referring to the console

• Unable to start RHEL6 in gui mode on IBM Flex System p460 Compute Nodes.