I have a 20" aluminium iMac from August 2007. Over the last couple of days it wakes from sleep, the screen comes on but the cursor is the spinning wheel. The hard drive makes a stuttering noise, as if it is trying to spin up to speed. I have to do a restart, at which point I get the flashing question mark folder. Again, the hard drive tries to spin up and keeps stuttering. I then have to turn it completely off, wait 2 minutes, and then it starts up fine. It works perfectly then, for hours, whether I'm using OS X or rebooting into Windows. I've done a full disk repair from the DVD, but it can find no problems. All permissions are fine. Sounds like the hard drive is on its way out to me, but I just thought I'd check before I pay a company to fit a replacement.