I found the HP Restore Manager and did a reinstall of win 10. It did not fix the problem. This is an HP T15. Here is the situation. If I start the laptop with the external power applied, after the HP logo completes the screen goes black. It appears like the LCD backlight turns Off. If I remove the external Power all is good. Replacing the external power again shuts Off the backlight. If I insert the external power with the backlight Off, press the Power button once, the laptop goes into sleep mode. Pressing the Power button again, the laptop displays the last page I was on and all is good. I have set the controls to never go to sleep or turn off the display while plugged in. I ran the HP Support Assistant and it did not find any out of date drivers. I am at a loss, any suggestions?