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 functioning, but all I see on the screen is a cursor against a black background.

In this situation, the only solution I initially found was to access tty1 by pressing Ctrl+Alt+F1 and restart the system by running sudo shutdown -r now.

A better approach, when Gnome crashes, is to restart only the window manager instead of the entire system.

You can achieve this by using the shortcut Alt+SysRq+K to restart Gnome and resolve the issue.