Given that the laptop worked while the screen on the unit was working, and that the external display also worked, the issue might be the OS not wanting to identify the original panel as the laptop's own display. You might want to unplug from the wall, disassemble the laptop, remove the battery, then the sticks of ram and press and hold down the power button for 30 seconds.
If you still can't get display on the original panel, then remove the CMOS battery and then replace it after 30 minutes.
Make and model of your laptop and it's SKU?