My toshiba M840 screen instantly goes black if power supply plugged in and would never turn on back. I've tried many method but none of that work , the screen goes black even in the save mode and I think it either the power supply problem or my motherboard. I hope I can find my solution here.
If it only goes black when you plug in the charger, I would go into "Control Panel" and then "Power Options". Next to the plan that is currently selected click "Change Plan Settings". Now click "Change Advanced Power Settings".
In here you want to check the options for the display and to be honest all the other settings, to make sure it isn't set to turn off the display when charging. Once you are done making changes click "Apply" and then "OK" and reboot the computer (turn it off and back on). See if this resolves the issue.