Replace BASEBAND power ic PM9645 located near audio ic at the backside of motherboard. If no repair history of phone then ur phone willb ok by PM9645 else u have to reball Baseband CPU. It can be done by professional only
Serial no is not there that means someone has repaired its NAND ic. If serial no present but no imei then it is issue of Baseband bt in ur case serial no not present but imei is there it is clear issue of NAND Data.
This component is not related to backlight section It is PN5.7 line which is aroung OL in diode mode and it generate by chestnut ic u r getting ur display image right if yes no issue of this line. Check anode line on display connector buddy.