Samsung Mega M819N DEAD!! , looking for experts advice on samsung hardware

Hi guys
*******r brought me a mega wanted a screen replacement and I did it and connected to charger so *******r can have it fully charge.
this morning wen I wanted to check it again and give it to customer, phone didnt turn on at all. when I turn it on Along with power supply it goes 10 20 and stay on 5. its not charging port, screen, camera, or any other connection because I check them all.
any good suggestions????