This has happened 2 times (rarely). Basically, when I wake up the macbook pro, the screen would remain "blank". I know the screen is on because I can see the mouse pointer but the whole screen is black. I'm assuming Finder has crashed? I don't know how to restart on the macbook (ctrl + alt + del didn't work, using option didn't either) so I just held down the power button for 4 seconds and restarted that way. Any idea why this happens?