If your data is backed up, try to repair your directory*:
If you do have a second Mac, and your data is not backed up, try Target Disk Mode to see if you can see the contents of your broken Mac:
and backup your most critical files that way*:
If your data is not backed up, and don't have a second mac, use Boomerang Boomerang, Prosoft Data Rescue II, or Subrosasoft Filesalvage and a Firewire external hard drive that is empty and at least as large as your internal drive to attempt to recover your data first before attempting to repair your directory.
In event none of these can boot your Mac, you may need to use the Startup Manager in the link below to boot them:
If your Mac still won't boot and you only have Apple hardware attached, start a new topic thread in the appropriate forum (Apple Discussions is divided into Categories which are then divided into forums), and tell us what you have tried and someone should get back with you.
- * Links to my pages may give me compensation.
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