I have an external USB hard drive; I plug it into my Mac, and I can clearly hear it turn on and start doing some work, but it isn’t mounted in Finder, nor is it detected by Disk Utility. It used to be detected just fine. Any tips on what I can do to get it back, if anything?
First, you need to prepare yourself for the worst: There is a good chance the drive is dead or dying. That said you do have a few glimmers of hope connected to this.
Power Supply Weak: It’s not clear to me whether this USB device is self-powered or requires an external power supply, but in either case the power supply could be weak and not giving the drive enough power to truly start up. If this is a case of the power supply being an issue, I would see if you can use another power supply and see what happens. If this is a self-powered USB case, it could be the computer you are connecting to is not providing enough power to the enclosure. I would see what happens if you connect it to another USB port or even disconnect some USB devices on the system to see if that helps alleviate any power load issues.
USB Enclosure Failing: The enclosure itself could be failing. Which means the drive inside of it is in perfectly good working order, but won’t be mountable until it’s placed in a new enclosure. Whether this is a 2.5” drive or a 3.5” drive, purchasing a new enclosure should cost you less than $10 at most. You would need to simply take the drive out of the current enclosure, put it in the new enclosure and away you go.
But if neither of those items helps, it could mean that the drive itself is dead. And if that is the case, there’s not much you can do.