This has happened two or three times to me in the past few months. (I have had my computer for less than 6 months). It is usually when I am browsing the net. The screen will dim, and a black window will show telling me in many languages that I need to restart my computer. There is the power button showing in the background of the box. I restart, and there is a message saying that the computer was restarted because OS X Unexpectedly Quit. Why is it doing this and how can I fix it?? Thanks!