Not sure if this has been mentioned before. I just purchased my MBA last week and I found out there's times I close the lid of my computer to do something else. But my MBA won't wake up after I open it up. I can hear something inside the machine. I had to hold down the power button for a few seconds till that noise is gone and press the power again to restart the computer. Is this a hardware problem or software problem? How do I fix it? Thanks in advance.