With the info you have provided, I'm guessing you have had a mainboard failure. If you haven't had the right
hand cover off and unplugged the display and not reconnected it properly, that is the only thing left.
Do all the leds flash or are they showing as though the are all jammed on?? From memory there are half a dozen
or more leds on the main board, in a line, that give you indication to the fault when it doesn't show on the display