The past few days my MBA 11 has been acting up. I will walk away from it and have a webpage open or something then I come back and the screen is black (i figure it just went to sleep or something) so I try to click the track pad or hit a key to wake it up, but nothing happens. The screen stays black. I can hear it running, but I can't do anything to get it to activate. The only thing that works is resetting it via the power button. It has done this both while plugged in and not plugged in. Any ideas?