I’m assuming you don’t even see the Dell logo splash screen but you can see a display when you connect to an external monitor.

I got this from a Dell Technical Support Representative:

1. Run LCD BIST
– Shut down computer
– Hold D & Power button at the same time
– You may see color changing display
– Please check if you are able to see any color like White, Red, Green and Blue

2. ePSA test
– Shut down computer
– Turn on back and quickly keep pressing F12
– You will see boot interface
– Please choose “Diagnostic”
– Kindly run diagnostic test and write down if there is any error message .
– Please check if you are able to enter to ePSA test

Contact Dell and tell them your observation.