This has happened to me a few times, so I'd like to find a solution.
After loading a game in full-screen mode, GFCE goes haywire. The screen goes black. The keyboard and mouse is still responsive, though. Hitting escape exits full-screen mode, but a translucent black forcefield prevents me from interacting with Gnome.
As far as I can tell, it is impossible to interact with the desktop or eliminate the black box. Ctl-alt-del and power button do nothing. So, a hard reset is required.
Does anyone have a solution? I will leave the "crashed" state live so I can attempt your suggested resolutions.
Here is a bad video of what I'm talking about.