Why does my external drive not show up?

An external drive that will not appear is alarming because of what is on it, and in most cases the disk itself is fine. Working through the chain in order tells you quickly whether this is a two-minute fix or a data recovery situation.

Safety

Step by step

1. Listen and feel before anything else.A mechanical drive should spin up quietly. Repeated clicking, grinding or a spin-up-then-stop cycle means a mechanical failure — unplug it and stop. Continuing makes professional recovery harder.
2. Try a different cable.Cables are the most common failure by a distance, particularly at the connector. Use a known-good one, and make sure it is a data cable rather than a charge-only lead.
3. Try a different port, directly on the machine.Not through a hub or a monitor. Hubs frequently cannot supply enough power for a mechanical drive, and that produces exactly this symptom.
4. Check power for a desktop drive.3.5-inch drives need their own mains adaptor. Check the light, the switch and the adaptor itself — power supplies fail far more often than drives do.
5. Try it on another computer.This separates a drive problem from a computer problem in one step, and is worth doing before changing any settings.
6. Look in disk management rather than the file browser.Disk Management on Windows, Disk Utility on macOS. If the drive appears there but not in the file browser, the hardware is working and the problem is the file system or the drive letter.
7. Assign a drive letter on Windows.A drive visible in Disk Management with no letter simply is not being presented. Right-click the partition and assign one. This is a common and completely harmless fix.
8. Recognise a file system mismatch.A Mac-formatted drive shows on Windows as unallocated, and Windows will offer to format it. Do not accept. The data is intact; you need software that reads that format, or a Mac.
9. Never accept an offer to initialise or format.Windows offers this for any drive it cannot read, including perfectly healthy ones in a foreign format. Accepting destroys the partition table and makes recovery much harder.
10. Try a repair only once the data is safe.Disk Utility's First Aid or Windows' error checking can fix a corrupted file system. Both write to the drive, so recover what you can first if the contents matter.
11. Check drive health.SMART data reports reallocated sectors and pending errors. A drive reporting problems should be copied off immediately and retired, whether or not it is currently readable.
12. Get help if the data matters and it is failing.A clicking mechanical drive with irreplaceable data is a professional recovery job. Repeated attempts to power it up reduce the chance of success.

Tips

• Label drives with their format and what is on them. Half of these problems are a drive formatted for a different system.
• A drive that has only ever been in one place is not a backup. If this incident was frightening, that is the actual lesson.
• Mechanical drives that have sat unused for years often will not spin up. Copy anything important off archived drives every few years.

Common mistakes

• Accepting Windows' offer to initialise the disk — It offers this for any drive it cannot read, including healthy Mac-formatted ones. Accepting wipes the partition table and turns a readable drive into a recovery job.
• Repeatedly powering up a clicking drive — Every attempt causes more physical damage. Unplug it and decide whether the data justifies professional recovery.

If it doesn't work

Questions people ask