Hello all, I have a 27" iMac and I've been making extensive use of the CTRL + SHIFT + EJECT shortcut to turn off the screen. Today, that shortcut stopped working. When I press those keys, the screen goes black, but after a few seconds, it's turned back on. Does anyone know where this problem comes from? I tried cutting off airport, mouse and keyboard, I tried restarting, but none solved the problem. Thanks.