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If your data is not backed up, and your drive suddenly becomes inaccessible or has errors which suggest directory issues, get Prosoft Data Rescue to attempt to recover data from your drive. Directory issues which Disk Utility and fsck can fix some of the time, and only third party utilities can fix other parts of the time, can be similar in symptoms to failing hard disks in that the entire drive becomes inaccessible. As such the first step is to make sure that your data is secure before attempting to repair anything. Once that is done, then you can see if repairing the directory with Disk Utility or fsck will fix the underlying issues of the drive. If Disk Utility can't repair the directory, with its Repair Disk function (i.e. you never get "The volume [My disk name] appears to be OK") then the next place to turn is Alsoft Disk Warrior.
Notes: If Prosoft Data Rescue is unable to recover information from the drive, and you don't have a backup, then I would seek a data recovery specialist and replace the drive that Prosoft Data Rescue won't recover from.
If Prosoft Data Rescue is able to recover all the information from your drive and/or your data is already backed up, but Alsoft Disk Warrior is unable to repair the directory, try an erase and install, and remember to keep frequent backups in case the drive does fail soon.
If you are able to repair everything, backup your data frequently in anycase, since you never know when a hard drive might fail.
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