Everytime you try to run Crysis you mean?
Happen with anything else?
It seems like you are pushing your monitor past its limits in resolution, or this is what seems to be happening.
You can fix this though.
Go to the game folder first. For instance, mines in 'E:\Games\Electronic Arts\Crytek\Crysis'
Within there you'll find a System.cfg file. Open this up.
Change where it says, for example on mine:
to something your monitor can provide, for instance 1280x1024, or, what you run your desktop at.
Then File, Save, and you are done!
If this happens however in the middle of a game and not just at start up, it could be leading to more serious problems. Especially if it is actually crashing your PC, and not just switching off the screen.
I hope this helps