I bought the monitor used a few yers back and its in good condition until today. The power source is fine bc my pc is working fine. There are LEDs on the button and they dont work either. The monitor is LG Flatron E2242TMake and model monitor?
Age, condition (new, used, refurbished)?
Are you sure that the power source (wall outlet, power strip, etc.) for the monitor is reliable?
Any LED's on the monitor? If so, do any of them light up at all?
Try a known working video cable. The monitor might just be on but a video cable problem may be preventing any actual display.
Otherwise it is likely that the power button has failed in some manner.
The power button may or may not be replaceable/repairable.