hi ,
i would follow these steps to get to the fix : (this advise on condition of no liquid spillage or physical damged )
# plug external monitor , use the hotkey to display the screen on both the international and external monitor and see , if still black . go step 2 .
# replace the screen , note: we have seen issues with the motherboard for this laptop , i would speak to lenovo as they might replace it under warranty if it is motherboard .
# all the best