Does the no video cables connected Self-Test and Built-in Diagnostics pass or fail?

U3223QE User's Guide pages 88/89.

The main display panel can't even turned on. There is no text or backlights at all, just pure black.

The only thing working is the while power LED near the power button.

* Disconnect every cable and USB device from the monitor
* Press and hold in the rear power button for 8 seconds
* Reconnect only the power cable and turn it on. Does the Self-Test no cable floating dialog box appear?

Yes, already tried without any cables. Even plugging out power, waited 5 mn, plug in back, power button hold for 8 secs. Nothing works.

Then some internal component has failed. Dell cannot know which component because Dell does not repair monitors. We only exchange them while still under the purchased warranty period.

Clearly, the display panel or the circuit driving it fails. We already had a Dell screen with the same symptoms in the past.

I will tell my employer to never buy Dell's equipments again. Other LG monitors in the office never have a problem.