shutdown/logout no working

when I try to shutdown/logout via the button on the panel, all my Icons from Desktop disappear, panels disappear, but the wallpaper stays and all the computer seems to be stuck in this state. the only thing I can do to continue is to restart the X server (Ctrl + Alt + Backspace), then the computer continues shuting down...
but when I type the command sudo shutdown -h now in Terminal, computer shutdown properly

can anybody help me how to make the shutdown button working?

I'm having the same issue now, it just appeared out of the blue. Possibly it started happening after I tried putting the computer in sleep mode once, but that's just pure guesswork.

Any ideas?