I found my x window is dead, all the graphic application have no reaction on the mouse click,so i have to change to the tty1 to work,use the Ctrl+Alt+F1 but the previous work is still need to rework.
The command ps doesn't display the xorg's thread, so I couldn't kill it.
And when I need to go back to graphic window, I must reboot the system.
From tty1 you can use the following command to restart only the GUI, without rebooting the system:
sudo service lightdm restart
or
sudo service lightdm stop
sudo service lightdm start
Another useful command in this case can be:
xkill # or xkill -all
(See man xkill to get to know how it works) and you can create a keyboard shortcut for xkill so you don't need to go in tty1 to use it.
