failed drive
When I got my new MacBook a few months ago, I was pumped. I loved it. I still do, actually. However, after one month, the hard drive failed. I went to sleep, MacBook running fine, and I was woken up by the sound of my fan going (I assume) as fast as it could go. My screen was on, and although the mouse pointer moved around the screen, when I clicked on anything I got no response. My dock animation still worked (I assume it was still in RAM) and my pointer was that stupid pinwheel/beach ball thing that everybody hates to see. I thought maybe it was crunching some serious numbers (although I have no idea why it would be) so I left it while I got ready for my day. I came back to my computer, only to find that it had done nothing.
I shut it off, and it never booted back up. It took a lengthy two minutes or so for the computer to realize that the hard drive was bad, and the flashing "question mark" folder came up. I called Apple, and they tried to troubleshoot a few things. It turns out that my hard drive was in fact a Seagate, and that it did in fact crash. Miserably.
Luckily, Apple replaced the hard drive free of charge, and they replaced it with a Hitachi.
Two months later, I'm still running fine!