Hi there, My Macbook (early 2008) froze and then I held down the power button to shut it down. Now it refuses to boot - it just stands on the greyish boot screen without any Apple logo ever appearing. I've tried resetting it by removing the battery and power adapter and then holding down the power button for 5 seconds. That didn't help. After being stuck on the greyish boot screen for a couple of minutes the fan starts blowing quite heavily. What can I do?