I have no idea what I did, but my Mac locked up, so I held the button to restart it and when I did a screen came up and stayed that has the power button symbol in the background and a message over it saying: "You need to restart your computer. Hold down the Power button for several seconds or press the Restart button." I know to hold down the Power button, everyone knows that, but what is the Restart button? I also tried just keeping it off overnight and booting up again, but that didn't work either. Thanks for any help!