My laptop Asus Rog Strix G531GT has been experience an issue with something. When I turn it on, the fan and HDD runs also the led is lit up. But no boot sound or screen (not always, but sometimes). But when I connect external monitor I can see the screen and signup window. I tried changing the project modes and also did reset windows. But nothing seems to resolve the issues. But when I restart or shutdown and turn on again, the laptop screen comes back with boot sound. Couple of months back, Asus changed the motherboard of my laptop under warranty because of an issue with sound output. This problem of not turning on the screen started few weeks after changing motherboard? Could it be a faulty motherboard or is it any issue with RAM or monitor itself? If monitor is faulty, then what can be the reason for no boot up sound?