The backlight of the display does light up only for a few seconds, one reason is a defective transformer in the inverter stage of the power supply.
In this case, a few windings of the transformer have an short circuit, causing the resistance of the two secondary coils to be different.
The fault of transformer can be detected by measuring the temperature of the transformer left and right side using infrared thermometer or thermal imager. The temperature will differ greatly.
Power supply model number is BN44-00238
Remove the display stand by removing the two screws on the round plate on the backside of the monitor
Open up the backside of the display (display placed face down on cloth to avoid scratches) by carefully releasing the snapped in latches using a screwdriver or opener tool.
The metal cage housing the PCBs as just stuck to the backside of the LCD.
Carefully remove adhesive strips, release the cables to LCD and front panel buttons.
Remove SMPS PCB (switching mode power supply) by removing screws around.
From power board desolder transformer. It has 6 pins on one and 4 pins on the other side.
Replace with new transformer.