how blank screen?

[gp_centos]

when my system turns down to sleep mode I get this window in the middle of the screen telling me there's no signal, how do I make the screen going blank? Thank you, george

[Whoever]

when my system turns down to sleep mode I get this window in the middle of the screen telling me there's no signal, how do I make the screen going blank? Thank you, george

It's the monitor that is doing this. Just wait. The monitor should go to sleep eventually.

[gp_centos]

Yes it does go to sleep mode but then it comes back and stays like that for hours. Also, at the top left corner it displays the HDMI mode icon.