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If you can't read anything on it, then it may be too far gone. I'd try to backup anything you can.
 
Suggest that you save all your work. Shut down all applications. Try to save what you can from the drive.

If you cannot read the drive at all, then shut down the Mac for a few minutes, then reboot. If you are lucky enough to see the drive this time, then copy your files right away. Select those most important to you first as you may not get a second chance.
 
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