DIAGNOSIS This is a complete power failure. The internal power board or DC-DC converter is dead.
FIX Unplug the monitor for 30 seconds. Plug it directly into a wall outlet, not a power strip. Press and hold the power button for 10 seconds. Plug it back in. Press the power button once. If nothing, the internal board needs replacement.
IF THAT DIDN'T WORK The power brick is integrated into the monitor. You need a qualified tech to replace the power supply board. Do not open the monitor yourself.
HEADS UP A dead power board often follows a power surge. Use a surge protector next time.