When you have the amp plugged in, and press the standby button on the amp itself, is there anything shown on the display, or is the red light on to the left of the display on?
This would suggest a power supply failure.
Could you try an alternative power lead or replace the fuse in the plug, and let me know if the red light and LCD display come on when you press the standby button?
Glad you got to the bottom of the issue, appreciate if you could rate the assistance you have received to date so I can close the case.
Have a good evening.