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 the cursor on the black screen.
In these cases the only solution I found was to access
tty1 by pressing
ctrl+alt+f1 and restart the system by running
sudo shutdown -r now.
The right 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 but remember that any unsaved file will be lost.