5 weeks old white MacBook 1.83GHz this afternoon, when i tried to start it 1. i pressed power button 2. I heard "chim" sound. the white apple screen did not show up, and stay that way Later, I managed to solve the problem by holding opt+cmd+p+r after pressing power. And so far, after several shut-down-start-again processes (twice), it looks ok. My question is: what caused the problem? BTW: I didn't add any RAM.