When an external drive doesn't appear, the cause is usually a cable, port, power, drive letter, or file system issue rather than a dead drive. The order of your fixes matters, though. Some common "fixes," such as formatting or initializing, can erase the data you're trying to reach. This guide starts with harmless checks and flags the steps that put data at risk. For a related guide, see Computer Has No Sound? How to Fix Audio Problems on Windows and Mac.
Start here: what exactly is happening?
"Not recognized" can mean three different things, and each leads to a different fix:
- Nothing happens at all: no light, no sound, no sign the computer noticed it. Suspect power, cable, or port.
- The computer detects it, but you can't open it: it appears in Disk Management or Disk Utility but not in File Explorer or Finder. Suspect a missing drive letter, unmounted volume, or file system problem.
- Clicking, grinding, repeated beeping, or a drive that spins up and down: stop. This points to physical failure. Repeated power cycling can make it worse, so skip to the data-safety section below.
Quick checks that rule out the easy causes
- Swap the cable. Cables fail more often than drives. Use the one that came with the drive if you still have it.
- Change ports. Plug directly into the computer, not a hub or dock. On a desktop, use a port on the back of the case.
- Check power. Desktop-class drives need their own power adapter and switch. Bus-powered portable drives can fail on weak ports or unpowered hubs.
- Test another computer. If the drive works there, the problem is on your original computer. If it fails everywhere, the drive, cable, or enclosure is the likely cause.
- Restart the computer with the drive unplugged, then reconnect it.
Fix it on Windows
1. Check Disk Management
Right-click the Start button, choose Disk Management, and look for your drive in the list (usually "Disk 1" or higher). What you see decides your next move:
- Healthy volume with no drive letter: right-click the volume, choose Change Drive Letter and Paths, click Add, and pick a letter. This is safe and often solves the problem.
- Disk marked Offline: right-click the disk number on the left and choose Online.
- Volume shows RAW, or the drive is unallocated or "Not Initialized": don't format or initialize yet. See the file system section below.
- Drive doesn't appear at all: go to Device Manager.
2. Reinstall the device in Device Manager
- Right-click Start and open Device Manager.
- Expand Disk drives and Universal Serial Bus controllers. Look for your drive, an "Unknown device," or an entry with a warning icon.
- Right-click the entry and choose Uninstall device. This removes the driver entry, not your data.
- Unplug the drive, wait a few seconds, and reconnect it. Windows should reinstall the driver automatically.
If the drive disconnects randomly rather than never appearing, power management may be the cause. Open Control Panel > Power Options > Change plan settings > Change advanced power settings > USB settings and set USB selective suspend setting to Disabled. This setting is mainly relevant on laptops, and turning it off may slightly reduce battery life.
3. Scan for errors
If the drive appears with a letter but won't open or reports errors, you can run a scan. Open File Explorer, right-click the drive, choose Properties > Tools > Check. Or run chkdsk E: /scan in a terminal, replacing E: with your drive letter. Repair options such as /f change the disk, so if the files matter and the drive seems unstable, copy off what you can first.
Fix it on Mac
1. Make sure it isn't just hidden
Open Finder, then Finder > Settings > General and tick External disks to show drives on the desktop. Under Sidebar, enable External disks too. A mounted drive may have been there all along.
2. Look in Disk Utility
- Open Disk Utility (Applications > Utilities).
- Choose View > Show All Devices so the physical drive appears, not just its volumes.
- If the volume is listed but greyed out, select it and click Mount.
- If it won't mount or behaves oddly, select it and click First Aid, then Run. First Aid checks and repairs the file system structure. Back up first if the drive seems unreliable.
3. Check whether the Mac sees the hardware
Hold Option, click the Apple menu, and choose System Information. Look under USB, Thunderbolt, or Storage. If the drive appears there but not in Disk Utility, try another cable or port. If it doesn't appear anywhere, the problem is likely power, cable, or the drive hardware.
On some Apple silicon laptops, macOS may ask whether to allow a new accessory to connect. If you dismissed that prompt, check System Settings > Privacy & Security for the accessory setting and reconnect the drive.
Drive detected but shows RAW, unallocated, or asks to be formatted
This is the riskiest situation because the prompt to format is the one thing that destroys data. Before clicking anything, work out which case you're in:
- Mac-formatted drive on Windows (APFS or Mac OS Extended): Windows can't read these formats natively and may offer to format the drive. Decline. Plug it into a Mac to copy the files off, or use a third-party driver tool if you must read it on Windows.
- Windows (NTFS) drive on Mac: macOS can read NTFS but not write to it by default. If the drive mounts but is read-only, that's expected behavior, not a fault.
- RAW or "unallocated" on a drive that previously worked: the partition table or file system may be damaged, or the drive may have been unplugged mid-write. Don't format or initialize it. Data-recovery software can often read files from a damaged volume, but the recovered files should go to a different drive.
Once your data is safely copied elsewhere, reformatting is the clean fix. In Windows, right-click the volume in Disk Management and choose Format. On a Mac, use Disk Utility's Erase. If you want a drive that works on both systems, exFAT is the usual choice. Erasing wipes everything on it.
When to stop and protect the data
Stop trying fixes and consider professional data recovery if the drive:
- clicks, grinds, or repeatedly spins up and stops
- was dropped, or got wet or very hot
- appears and disappears repeatedly, or becomes extremely slow when you open folders
- holds irreplaceable files and fails every test above
Don't open the drive casing, and don't keep reconnecting a drive that makes mechanical noises. Reputable recovery services usually offer a diagnosis before you commit to a price, so ask about that and the fee up front. If the drive is still under warranty, the manufacturer's support page will explain the process, though warranty replacement does not recover your data.
Confirm it's fixed
Don't stop when the icon reappears. Open the drive, copy a few files to your computer, and open them to confirm they're intact. Safely eject and reconnect the drive once to check it mounts reliably. If it works but has been flaky, copy everything off now. Keep important files in at least two places, because an external drive on its own isn't a backup.
What to do next
Work from the simple to the risky: cable, port, and power, then Disk Management or Disk Utility, then error checks. Never format, erase, or initialize a drive whose contents you still need. If the drive is physically failing or every software check fails, stop and get recovery help before attempting anything else.