I had the same thing happen and was convinced that my brand new computer was toasted. What eventually worked was to hold down the power button until I could hear that the system had been turned off, and then hit it again to start it up again. All has been well since. My working theory for this is that because the power level was low, it decided to hibernate. The problem is, I can't explain why it then would not start up when I plugged an adaptor in. I'm wondering if there is a power glitch.