This has been happening for the past 2 weeks or so. Periodically, while I am actively using the computer (browsing the web, typing in word, etc.). The screen goes black, as if it is sleeping, but I am in the middle of doing something, the computer is not idle. The only way to "wake it up" is to plug it in. Though, the last time it did this, it was plugged in, and I had to shut it down by holding down the power button, because it was otherwise unresponsive. The battery is not low, no warning has come up about using reserve power, or needing to plug in. It is very frustrating! What is happening, and how can I fix it? Should I just call applecare, or bring it in?