I have a HP desktop machine with Ubuntu 14.04, with also Xubuntu and Gnome desktops installed. I mostly use the Xubuntu session.
When using the Xubuntu session, when I power off my monitor, and power it back on, the screen stays black and I cannot do any work. With ctrl-alt-f6 I can open another virtual terminal, and then the screen works again, but if I to go back to the desktop session with ctrl-alt-f7, all I have is a black screen.
But, if I login to Unity (the Ubuntu default session), or to Gnome, and turn the monitor off and back on, everything works ok. Also, if I log out, and while in the lightdm greeter, turn the monitor off and back on, everything works ok.
What could be the cause for this, and how to fix this?