I have a 13" Macbook that goes to sleep randomly. It would be more precise to say that it "hibernates" randomly, because when the Macbook shows this behavior, pressing the enter key or moving my finger on the trackpad won't wake it up. Additionally, the light on the front of the computer goes off. The only thing that wakes the computer up is closing the laptop entirely, waiting for the light on the front to go back on (it goes into that mode where it fades brighter and dimmer), and re-open the machine. This seems to be more likely to occur when I'm moving the laptop while it's open, but it's also happened occassionally when I've just tapped the machine or even normal typing. I don't recall it ever happening when the computer was completely stationary. Does anybody have some ideas regarding what might be causing this? Thanks.