Mobile isn't turning on after turning of while charger pluged

Hello,

I tried to root my mobile and it root after that i tried to unlock bootloader and it also unlocked while my mobile was plugged in to my computer i turned my mobile off after that i tried to turn it on but it not turned on.

i took it to a mechanic and he told me that its display panel will be replaced i quite surprised that hows this happens. i didn't believed on mechanic.

Please Tell me what to do.

Sorry for bad English.