One of two things has failed:

The backlight in the display, or

The high voltage circuit that powers the backlight.

The only real way to tell which is going to be to check the connector that supplies power to the backlight inside the system with a VOM.  

Hi @SConlee  it would have helped if you shared what laptop you are working on.

From what you say it seems to be old, has been in constant use, and can still be used with an external monitor. You have successfully identified the problem as being the screen's backlight lamp and/or inverter. Usually its the backlight lamp that has come to the end of its life and requires replacement. Tapping on the back of the screen probably broke the lamp. 

Unless you have new or used parts available locally, there seems no alternative but to keep using the monitor until a backlight lamp and/or inverter can be purchased. There are many videos on the internet and YouTube usually provides information on your laptop model series. If you want to save the YouTube video, insert a double "s" in the url web address, for example https://www.youtube.com/watch?v=ucaJA324hbg becomes https://www.ssyoutube.com/watch?v=ucaJA324hbg. Being on deployment at sea should not stop you ordering replacement parts. 

Its only a month old though and has been used for maybe 20 hours.

Awesome thank you. Where would I find those connections and what voltage should I see? Additionally if I see no voltage I am assuming that tells me the High voltage circuit is bad and if I see voltage then I am assuming the display is bad?

Laptop is AlienWare M17 R3 if that helps

That changes the calculus.  It needs to go back to Dell for warranty repair.  

There is no inverter in the system -- those came with old style CCFL backlights.  Systems with LED backlights (just about anything made in the last 10 years) do not have inverters.  The high voltage circuit that powers the LEDs is integrated onto the system board.

Since you have at least 11 months' warranty remaining, contact Dell when you're available and schedule a repair.

Hi @SConlee thank you for sharing your laptop designation. Unfortunately the Alienware m17 R3 Service Manual does not include how to replace the screen's backlight lamp and/or inverter. Visiting YouTube should provide the video. 

Wow, m17 R3 only a month old and has been used for maybe 20 hours. If more than 30 days since the Dell invoice date, you have lost the option to Reject and get a full refund, and you are stuck with the Dell Warranty to provide replacement parts. ‎Dell Refund policy, New vs Refurbished | DELL Technologies. 

Try getting in touch with your Dell vendor and ask them to provide a brand new m17 R3 replacement because this Dell system is clearly not fit for purpose and should never have been sold to you. Please share their response in this forum. Thank you. 

@ejn63​ 

hi can u help me ? I have the same problem . I have r17 m3 , the board burned up .. I change the Board to second hand .. the laptop boot up .but black screen, works only with external hdmi .. 

I change the lcd and cable for new !! And still same! Black screen .. then I realized that the board that I install it’s 300h . And I had before 144h .. so i ordered new lcd and screen of 300h . I install it now .. and the screen works but with no backlight .. it dark . Only with flashlight I can see . Can u tell me or help me where is the problem .. thanks