RE: my dell latitude e6420 screen goes blank when it has to boot
I recommend you to remove static charge. For that remove the battery and disconnect the ac adapter, press and hold the power button for 20 to 30 seconds. Now connect only the ac adapter and wait for 30 seconds and turn on the system. This will drain any residual charge in the capacitors.
Also check if you can run diagnostics on the hardware components of the system. Press and hold the Fn key on the keyboard and power on the computer to launch diagnostics. Refer to the following link for assistance:
Reply to the post in case of any error message.