Western Digital hard drives can become "locked," meaning that you will be unable to modify or delete any of the files that are currently installed to the drive. This is a protective measure that can be used when connecting the drive to a computer of questionable standing, preventing spyware and other viruses from infecting your WD hard drive. Changing this requires that you flip the jumper on the back of the drive.
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Power down your computer.
Remove the screws on the rear of the case and remove the side panel.
Place the jumper on the back of the hard drive to the "write-enabled" position. Consult your drive manual if unsure of how to do this for your specific Western Digital drive model.
Replace the side panel and restart the computer.