AW3420DW, black screen

Got my new AW3420DW 34" screen 24h ago.

Was working fine, until today when screen went gray with the "no signal" message. I restarted the computer but then the screen went black, with blue power LED, and nothing happening.

I tested the PC with another screen, same DP cable, it works fine.

Going back to the AW3420DW, it is stuck on black screen / blue power LED even if all cables except power are disconnected. If I press on the screen power button, it goes off and then I can not bring it on again, I have to unplug and plug the power cable to recover the black screen / blue power LED situation.

In brief, short of sending the screen back, what can I do ? Looks like deep sleep / little death to me.