The most useful diagnostic tool you own is thirty seconds of patience. Connect the drive, then do nothing: watch whether the LED lights, lay a finger on the casing to feel for the faint vibration of platters turning, and listen hard. What you observe sorts the problem into one of three boxes — a connection issue that costs pennies, a corrupted file system that needs care, or failing hardware that needs a lab — and everything sensible you do next depends on which box you're in.
One observation overrules all the others. A drive that clicks, chirps, beeps, or spins up then dies again in a loop has a mechanical problem: dying read/write heads or a stuck spindle motor, very commonly after a knock or a fall. Powering it again grinds delicate heads against the surfaces that carry your files. Unplug it, keep it flat and still, and jump ahead to the final section.
Start where failures are cheapest. Swap in another USB lead — the ones boxed with portable drives are famously flimsy — then move to a socket on the computer itself rather than a hub, monitor or front panel, then borrow a second machine if there's one about. A desktop drive with its own mains adapter deserves equal suspicion of that adapter: no spin whatsoever often means a dead power brick rather than a dead disk.
On Windows, the honest picture lives in Disk Management, reached by right-clicking Start. A disk listed there yet missing from File Explorer may only need a letter — assigning one via 'Change Drive Letter and Paths' touches nothing important. The dangerous branch is different: a disk reading RAW or 'unallocated', or a prompt to initialise, means the file system has broken. In most cases the files sit intact behind that broken index, and every rescue Windows offers — initialise, format, repair — writes over the structures an engineer needs. Refuse the lot.
Mac owners should open Disk Utility and switch on View → Show All Devices. Hardware present with a volume that won't mount is a common sight; the traps are Erase, which is exactly what it sounds like, and First Aid on any drive making new noises, since repair passes push failing mechanics hard. Rule out one false alarm too: a disk formatted NTFS for Windows won't behave on macOS, and an APFS disk means nothing to Windows — the data is fine, it's just sitting on the wrong platform's desk.
Seagate portables produce a specific pattern: LED on, sounds normal, appears nowhere. Nine times out of ten that's the USB bridge board or its firmware sulking rather than the disk — new cables won't cure it, but bench equipment reads straight past it. WD's My Passport and Elements ranges hide a different trap: the bridge encrypts on the fly, so shelling the disk out of its case and cabling it up bare gets you ciphertext, not files. Recovery has to go through that original board, or reconstruct what it was doing.
Whichever brand you own, end the replug ritual. A drive that mounts on the fifth attempt today and the fifteenth tomorrow is failing on a schedule, and each retry burns some of the remaining life you would rather spend on the recovery itself.
Draw the line at any of these: noises after a drop; a RAW disk holding files you can't lose; detection that keeps getting rarer; a recovery app that has scanned all night for nothing. Past that line you're gambling the data to dodge the cost of finding out — and finding out here is free.
Pack the bare drive well, post it tracked, and inside 2 working days of it reaching the bench you'll have a diagnosis, an honest list of what's recoverable and one fixed figure to say yes or no to. The full service lives on the external hard drive recovery page; alternatively, open the free online diagnostic and tell us what happened.
If it clicks, it stops. No noise a drive makes improves with running time, and failed heads will score the surfaces your files sit on. Power down once, stay down.
The diagnostic is free, the quote is fixed, and logical faults run no fix no fee. Start online or ring the freephone.