There are three LEDs on the front of your ImageCue.  Here's what they indicate and how to use them to troubleshoot:

 ♥ (Heartbeat) - This blue LED flashes once per second to indicate that the ImageCue control board is operating properly.  This LED is independent of the Raspberry Pi 2.

PI - This blue LED flashes every time the Raspberry Pi receives a packet of data from the ImageCue control board.  This LED is directly controlled by the Raspberry Pi 2.  The rate of flashing should match the DMX LED except during RDM data exchanges.

DMX - This green LED flashes every time the ImageCue control board receives a DMX512 packet (can also be RDM).  This LED is independent of the Raspberry Pi 2.  The rate of flashing is an indication of the DMX512 refresh rate.

If the LEDs are disabled (turned off) by the Setup Menu they will NOT BE VISIBLE.  Also note that when turning the LEDs on or off the mode does not change until the Setup Menu has been exited.

During normal operation the blue ♥ LED will flash once per second, with the blue PI LED and green DMX LED flashing rapidly.  If the green DMX LED is not flashing (the blue PI LED will also stop) the unit is not receiving DMX512 frames.  The LCD display will most likely display "DMX Reception Lost".  The green DMX LED will flash as long as DMX512 frames are being received - even if the DMX start address is not correct for your setup.

If the green DMX LED is flashing but the blue PI LED is not, it is possible that ImageCue is handling RDM commands such as "Identify Device".  The LCD display should provide some information in this case.  Otherwise, it is likely that the Raspberry Pi 2 has crashed or not started up.  If the LCD display is showing "Waiting for Pi!", the Raspberry Pi has not started up.  Please refer to the article "Waiting for Pi!".

There is more information about the LEDs in the ImageCue Model 1.1 User's Guide.