Well, through trial and error I have narrowed it down to this: Using my mac mini 1.83-C2D and ipod shuffle, the computer will not boot. In other words, -If I boot with the ipod in its dock and the dock plugged into the computer, The apple/swirly circle takes a while and then leaves me hanging at a light-blue screen. If I remove the ipod from its dock, the boot process immediately continues as normal. -If I boot with the ipod removed from its dock or the dock unplugged from the USB port, the boot process is normal. All updates are installed on the mac, I restored the ipod to factory settings, and it is plugged in directly to the back of the mac (not through a hub). I'm wondering if there's some kind of miscommunication, where the computer can't decide if it's trying to boot from the HDD or the ipod?? And it gets stuck. Other USB peripherals are not causing it. I can't figure it out.