Restart Gnome on Ubuntu 12 (Precise Pangolin)

I use Ubuntu on a Lenovo Thinkpad X1 laptop and sometimes Gnome becomes unresponsive after sleep mode. The system is working, but I can’t see anything except for the cursor on the black screen.

In this case the only solution I found was to access tty1 by pressing ctrl+alt+f1 and restart the system by running sudo shutdown -r now.

A better solution when Gnome crashes is to restart only the window manager, not the whole system.

To do so you can use the shortcut alt+stamp+k to restart Gnome and the problem is solved.