My new MBA doesn't seem to want to wake up from a long sleep ! If it sleeps during the day (1-2 hours between wake-ups), then it's OK. If it sleeps overnight (8 hours or so), then when I open the lid there is a faint glow from the screen but little else. I usually have to reboot via the power button. How long should I wait after waking it from a long sleep before using the power button ? Are there two different sleep modes - fast wake up and slow wake up ?