After hassle to set up my "Shuttle X50V2 Plus" as MD (network adapter problem, screen resolution, etc. ..), it now works (thanks for the information found on the wiki).
But is there a reason why "DPMS monitor" does not work properly, knowing that this MD has an Intel video card (lmce 10.04)?
The screen turns off and comes back right away.
I know that Intel card is currently not recommended but that Shuttle seems perfect for integrating my kitchen! ;-)
And I think it's the only way to turn off the screen when I do not use it.