**SOLVED** I have an external hard drive that was working fine until recently. No idea what changed (didn't disconnect it, update the Mac OS, anything). Now I can see it in system profiler, but not in Disk Utility or Finder. Have tried restarting with it connected, and without it connected, and also switching USB ports. Not sure where to go next. I cannot format it because it has all of my photos (my entire iPhoto library) on it. I do have a second back up, but I discovered this issue as I was preparing to update it. And my third backup is Facebook, which would take FOREVER to download and reclaim all my pics.
Solution: While USB plugged in, unplug the hard drive's power from the wall or from the drive itself. Wait for it to completely quiet (10-15 seconds), then plug power back in.
Solution: While USB plugged in, unplug the hard drive's power from the wall or from the drive itself. Wait for it to completely quiet (10-15 seconds), then plug power back in.
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