not help in teh sense but there is a way to close a task even if you don't see the task manager (believe me, it opens even if you don't see it ,p)
to do that you have to hit
ctrl + shift + esc (all 3 at the same time, in that order, hold ctrl shift and then esc then let go of em) (Make sure the processes tab is selected beforehand because that is the most important tab of them all) it remembers which tab is selected in the task manager, so do this first and then try in the game ;p
Anyway, that combo opens the task manager (even if you don't see it)
now type -> "AVW" in quick succession. .. so just A V W
and hit "ALT + P" (that's the combo for closing the task you selected by typing its name... sorta)
then hit Enter key (thats the "yes close this task" action)
Does this get you out of this black screen situation? Because if it does, it is not a hard-lock. If it does not, you are looking at some kind of hardware/driver malfunction.
In any case, that it does not give you your screen back or control back is obviously a pretty big bug somewhere.. but where I do not know.