AW3821DW : screen is turn on but remain black - no OSD

I have bought 2 month ago this screen.

It is great :)

But it worked well for 2 weeks. after that, the screen did not wake up after a sleep. I had to power it off and on.

Two weeks later after my vacation it becomes worst.

When I power on (or when the screen is in sleep mode for more than 5 minutes), it do turn on (I can see the back light - but the screen remain black, with no OSD).

I have a dual screen set up, so I still manage to use my PC with the other screen. And if I put a windows "in the AW3821DW" screen I can see some light effect.

But the screen remain black.

At first it did wake up after 1 or 2 hours like if everything is working.

So I began to never power of the screen and deactivate the sleep more.

It worked fine for several weeks (without sleep).

But I had to leave severals days last week. So I powered off the screen and the pc.

And now, since my return, the screen remain black without OSD even after 24 hours.

Of course, I already change the display port cable, turned off the minitor, the pc, unplug everything, hold the power button for more than 10 seconds. But nothing works.

The screen stay "black" with the back light but no OSD nor images I can see.

I hope you will be able to help me.