Typically, you will see this behavior when the MP500 boots up in recovery mode. This will generally happen as a result of one of two things.
1) When powering on the MP500, if you hold down the power button for longer than 2 seconds, the MP500 will boot into recovery mode. This will be accompanied by the LED on the power button blinking repeatedly.
2) The MP500 has two separate HDMI ports on its front panel. In general use, any HDMI connection being made with the MP500 should be made through the AUX1 port, rather than the AUX CPU port. Making a connection to AUX CPU will cause unexpected behavior, such as the MP500 booting into recovery mode.