My MBA 11" 2012 just froze. Screen is frozen, mouse pointer is stuck, caps lock button doesn't light up. Even when I press the power button, nothing happens. I tried closing the lid to put it to sleep. It went to sleep, but when it came back it's still stuck. Can someone tell me how to restart the system and what's causing it? It's a new MBA 11 with no software installed. I was just browsing the web (in Safari) when it happened.