Why my laptop is not turning on when power button is pressed?

I have Haier Laptop Model 7G-5H. It’s runny without any battery and directly powered by AC Adapter. When adapter is connected, the charging light shows on simply indicating the power is through the laptop but when I press the power button, nothing happens (maybe a small buzzing sound), not like fans turning on or something - no LED on power button turns on. I’m stuck here. I disassembled the laptop and cleaned the ribbon connecting Power Button to Main Motherboard and refixed but to no avail.

Kindly give guidance.