Troubleshooting Start Disk
From Applepedia
If your Mac doesn't find a boot disk, it'll show a floppy disk or a folder with a blinking question mark. If it finds a bad boot disk, it'll show a floppy disk with an x, or a folder torn in half.
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Boot disk listing
- Hold down the option key on boot, and see if any disks show up there.
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Bad hard disk
- Try booting from your Mac OS system disk, and use Disk First Aid or Disk Utility to determine if your boot disk is OK.
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Incompatible system version
- If you're booting from a CD or DVD, make sure it has a version of the Mac OS appropriate for your model.

