A while ago my laptop monitor stopped working, but it is working just fine if you connect an external monitor. There is a backlight but no image, I have tried to upgrade BIOS and all the drivers but nothing seems to work... So I suppose it is a hardware problem, but what do you think broke? The display itself or the cable between the display and motherboard? Or can it be a software issue I have missed?
First you may want to check the ribbon cable that connects the LCD to the motherboard if it's seated properly. You can unplug/replug the ribbon cable on both ends just to make sure everything is seated properly. If it doesn't work that means it's the actual display that is faulty an replacing it would be the only solution unfortunately. If it's still under the factory warranty do contact Asus for a repair.