Either Firmware is misreading information from LCD circuit board  or something is loose in side(less likely to happen)  Updating BIOS is your only option.  If already updated try Flashing the same version one more time.  Last option before you open your computer to see any thing is loose.  Perform a BIOS RECOVERY , if fixes most of the Firmware Bugs 
Hello, I have had an XPS 15 7590 for a couple years.I have a dual boot solution with Windows 10 and Ubuntu, never had any issues until today. Today, after an update from Windows, the computer would not start and showed me a blinking front led light, alternating 7 white and 2 amber blinks. I tried force rebooting, and got the same result, only that after a while it booted into Ubuntu, skipping the Dell splash screen and Grub boot selection screen.The laptop shows no issues whatsoever, working properly as usual in Ubuntu, but restarting I still cannot get the BIOS to show anything on the screen, first thing that appears is the Ubuntu login screen. After some googling I found out the problem is related to LCD failure, but the screen is working just fine, since I am using it through my Ubuntu OS to write this right now. Furthermore, I tried to run the system LCD BIST test, which showed the flashing colors as it is supposed to do, so no issues there. It seems to me that the faulty Windows update has somehow broken something related to the ability of the BIOS (and Windows) to communicate to the LCD screen. If I connect my laptop to an external screen via an HDMI cable, I am able to fully operate the laptop as usual, although with the led blinking still detecting an LCD failure, as the system recognizes the external screen as the main (and only) screen. I was able to log into Windows and found no issues in the system, running all Dell repair tools, checking everything was up to date (Dell Update, Windows Update, Nvidia GeForce). I tried to reboot the laptop after the updates, hoping the issue would go away, but it has not. I also tried to reflash the latest BIOS update, but the problem is still here. So to sum it up, I have a working LCD screen (that I can use through Ubuntu), a working BIOS and Windows system (that I can use through an external screen), but the two do not seem to get along very well.Provided that I can still use my XPS with an external screen, I would like to know if there is something I can try to recover the use of the LCD screen of my laptop. Thanks for any suggestion you may have.
XPS 15 7590 detects LCD failure but screen is working