There is a series of LEDs on your board, near the center.
They are labelled VBB ( red ), 3.3V ( orange ), and 1 2 3 and 4 ( all green ).
We are still only interrested in the green LEDs.
Different behavior can represent different situations and problems for the board :
Normal pattern
If your LEDs do this :
Then the firmware is running, and the LEDs are displaying correct behavior.
Click on Normal pattern
SD card problem
If your LEDs do this :
Then the firmware is running, but the board encountered a problem reading or accessing the SD card, or the configuration file on the SD card.
Click on SD Card problem
Firmware crash
If your LEDs do this :
Or this :
Then the firmware is not running.
Click on Firmware crash