Your external drive was working yesterday and today it's invisible — no letter in File Explorer, no error, nothing. Don't panic and don't format anything yet. The drive's data is usually fine; it's the connection or the partition table that's confused. Work through these in order.
1. Rule Out the Obvious
Try a different USB port — preferably one directly on the machine, not a hub. Try a different cable; USB cables fail silently all the time. If you can, try the drive on another computer. If it appears elsewhere, your drive is fine and the problem is on the first machine. This thirty-second test eliminates half of all cases.
2. Check Disk Management
Right-click Start > Disk Management. If the drive appears here but not in File Explorer, it's usually one of two things: it has no drive letter (right-click > Change Drive Letter and Paths > Add), or the partition shows as "Unallocated" or "RAW." If it needs a letter, you're done in ten seconds. If it shows RAW or unallocated, do NOT format yet — read step 6 first.
3. Power Problems
Spinning external drives are power-hungry. If you're on a laptop running on battery, or the drive is plugged into an unpowered hub, it may not be getting enough juice to spin up properly. Plug the laptop into its charger, connect the drive directly to the machine, and for larger desktop-class drives use the powered USB hub or Y-cable they came with.
4. Reinstall the USB Drivers
In Device Manager, expand "Universal Serial Bus controllers," right-click each USB Root Hub and Host Controller, and choose Uninstall device, then restart — Windows rebuilds them fresh. Also check under "Disk drives" for your external drive with a yellow warning icon. Corrupted USB drivers after Windows updates are a classic cause of vanishing drives.
5. Check the BIOS
Restart and enter the BIOS/UEFI setup. If the drive doesn't appear there either, the machine genuinely can't see it at the hardware level — suspect the cable, the enclosure's bridge board, or the drive itself. If it does appear in BIOS but not Windows, it's a Windows/driver/partition issue, which is much more fixable.
6. Recover Before You Format
If Disk Management shows the partition as RAW or unallocated but the drive is detected, your files are probably still on the platters. Try TestDisk (free) to rebuild the partition table, or Recuva/PhotoRec to pull files off before doing anything destructive. Only format as the last resort, after you've recovered what matters — formatting a RAW drive destroys the file index.
7. Enclosure vs. Drive
If the drive clicks, beeps rhythmically, or spins up and down repeatedly, that's the drive mechanism failing — stop powering it on repeatedly, and if the data matters, talk to a recovery service before it gets worse. But if the drive sounds normal and just won't mount, the USB bridge board in the enclosure often dies before the drive does — removing the bare drive and connecting it via a SATA-to-USB dock (or internally on a desktop) frequently brings it straight back.
One prevention note for the future: drives run hot during long transfers, and heat is what slowly kills them — keep transfers in a ventilated spot, and on the laptop side a proper fan-control setup keeps the whole system (and the USB power delivery) stable during those multi-hour backup sessions.