How do I recover files from an internal hard drive that is no longer recognized?

Question

Hi there,
Any help on this problem is greatly appreciated!  I have a MacBook Pro (late 2009) running Snow Leopard.  Over the last few years, after having brought the computer in to get checked, it seems that the RAM cards have gotten loose (or the bottom cover of the computer gets loose) and occasionally a grey curtain will come down from the top of the screen and everything stops working.  Restarting the computer is often fine but sometimes it can't be restarted and I have to take the cover off, reset the RAM cards in their slots, and retighten the cover.  The computer usually works fine after that, but verifying the disk using Disk Utility will sometimes indicate there is an error and the disk needs to be repaired.  Repairing it in Disk Utility is usually fine.
Last year this happened but the disk could not be repaired. The operating system could still be run, and after making a backup of all my files I reinstalled the operating system from the installation DVD, which didn't delete any of my files on the hard drive anyway.
A few days ago the same grey curtain issue happened, however upon resetting the RAM and back cover and restarting the computer, the apple logo appeared which was quickly replaced by a prohibitory sign, which stayed on the screen indefinitely.  After putting in the installation DVD and trying to reinstall the operating system, when the option comes up to choose which disk to install OS X on, the internal hard drive does not appear as an option.  Going to Disk Utility from the DVD, the internal hard drive appears on the left but the text is greyed out.  Attempting to repair the disk gives the following error message:
Checking Journaled HFS Plus volume.
Invalid key length
Invalid record count
Catalog file entry not found for extent
The volume    could not be verified completely.
Error: Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.
While I know I could completely erase and reformat the disk, I really don't want to lose any of my files (ideally).  If I erase the disk but select "Don't Erase Data" from the "Security Options..." in the "Erase" tab in Disk Utility, will this keep all my files in tact and will I be able to access them later?  Are there third party applications that can recover my files so I can make a back up before I delete and reformat the hard drive?  I am currently running the computer through an external hard drive connected by USB, but the internal hard drive still doesn't show up in Finder (only in Disk Utility as greyed out text).
Can I recover my files?
Thanks so much!

Answer 1

Try using a data recovery product such as the ones listed here. Don't erase the drive or write anything else to it until the files are recovered or you choose not to recover them.
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