Everything from a five-pound lead to a seized motor produces the same blank window, which is why guessing is expensive here. Work through the hurdles in order and you will know roughly what you are holding within a few minutes, without spending any of the drive's remaining life to find out.
Between the socket and the icon on your desktop, a USB drive has to get past three things in sequence. It has to receive enough power to spin up or wake up. The computer then has to notice that a storage device exists on the bus at all. Finally the volume on it has to be readable well enough to be mounted and given a name. Nothing appears until all three are cleared, which is exactly why the failure looks the same however different the causes are.
Each hurdle leaves its own evidence. Power shows itself as an LED, a faint whirr, or a slight resistance you can feel through the shell if you rest a fingertip on it. Recognition shows itself in Device Manager on Windows or System Information under USB on a Mac, where a drive can be listed as a device even when no volume ever mounts. Mounting is the part you normally see, and it is the last to happen. A drive that is warm and turning but absent from Device Manager has failed at hurdle two, which points at the bridge electronics or the disk's own firmware, not at a cable. A drive that is listed as a device but has no usable volume has failed at hurdle three, and that is usually a filing problem rather than a hardware one. Sorting the fault into one of those three buckets is most of the work.
Before any of that matters, listen to it for ten seconds with the room quiet. Regular ticking every second or two, a short rasp followed by silence and then the same again, a repeating spin-up that never settles, or a run of electronic beeps from the case — any of those means the mechanics are involved. The ticking is the head assembly sweeping across and being reset because it cannot find its bearings. The beeping is a motor drawing current it cannot turn into rotation, usually because the spindle has seized or the heads are resting on the surface and holding it.
This overrides everything else on the page. Heads that are not reading properly are still flying a fraction of a micron above the platters, and once one has made contact it takes material with it and spreads the debris around the inside of the drive. That damage accumulates every second the thing is powered, it never repairs itself, and there is no combination of software, freezer myths or firm taps that reverses it. Switch it off at the wall, leave it off, and go straight to the last section. Everything in between is written for a drive that is silent.
Assume the least interesting explanation until it is ruled out, because the least interesting explanation is right more often than the impressive ones. Start with the lead. Bundled USB-C cables are built down to a price, and plenty of the spares in a household drawer are wired for charging with the data pairs missing altogether, which produces a drive that lights up and is never seen. Borrow a lead you know carries data rather than inspecting the old one hopefully.
Then the port, and here the issue is usually current rather than data. A bus-powered 2.5-inch drive can pull more at spin-up than a front-panel header, an unpowered hub or a monitor's built-in socket will deliver, and a drive that browns out mid-spin-up will drop off the bus and reappear in a loop. Go straight into a port on the back of a desktop or directly into a laptop, and if the drive came with a Y-cable, use both ends of it. After that, try a different computer entirely: that one step separates a fault in the drive from a fault in a driver, a chipset or a USB controller, and it takes under a minute.
Mains-powered desktop units deserve their own paragraph — a Seagate Backup Plus Hub, a WD Elements Desktop, a Buffalo DriveStation, a G-Technology G-Drive and anything else with a barrel connector on the back. Where there is no light, no movement and no sound whatsoever, the small external power brick has failed far more often than the disk inside has. They are the most common non-fault described down this freephone. Match the voltage, the current rating and the polarity symbol printed on the label before borrowing a supply from something else, because putting 19 V into a 12 V unit turns a ten-pound problem into a board-level repair.
Inside the shell there are two devices, not one. The disk speaks SATA or NVMe; the outside world speaks USB; a small bridge board in between does the translation and has its own power section, its own firmware and its own failure modes. When that board dies you get the classic pattern from hurdle two: power reaches the disk, you can feel it spinning, and no computer anywhere will admit a device is attached. On the bench the disk is simply connected directly and the bridge is left out of the circuit, which is why a unit that looks utterly dead on a kitchen table is often an unremarkable job.
That is not an argument for prising the case open yourself, and there is a specific reason. On a great many current portables — most WD My Passport models, several SanDisk and Samsung portable SSDs, various rugged ranges — the encryption is done by the bridge, not by the operating system, whether or not you ever set a password. Pull the bare disk out of that shell and it reads as random noise on any machine on earth, because the key material lived on the board you have just discarded. Send the unit whole and intact and let the pairing be preserved by somebody with the equipment to work with it.
One habit is worth breaking while you are here. If the drive appears on the third attempt this week and the eighth attempt next week, it is not being temperamental, it is failing gradually and telling you so. Every mount you spend proving it still works is one you cannot spend copying files off it. Use those attempts for the folders that matter, largest and most important first, and stop as soon as it drops out.
Explorer and the Finder both present a tidied version of the truth in which broken things are simply absent. The unedited view on Windows is Disk Management, on the menu when you right-click the Start button. A disk that appears there with a healthy partition and no letter beside it has usually just lost its drive letter in a clash, and assigning a new one is safe and instant. The description to be careful about is RAW, or unallocated, or a pop-up asking to initialise the disk. All three mean the same thing: the structures recording where each file starts and stops are damaged. They do not mean the disk is empty.
Decline the offer to initialise, and decline the offer to format that Explorer will make separately. Both write fresh structures directly over the damaged ones an engineer would otherwise use to rebuild your folder tree, and Windows will keep asking every time you plug it in without ever taking no for a final answer. Treat chkdsk with the same caution on a drive holding anything irreplaceable: it is designed to make a volume consistent, not to make it complete, and it will happily discard what it cannot reconcile.
The Mac equivalent is Disk Utility with Show All Devices switched on under the View menu, which reveals the physical device above the volumes sitting on it. A greyed-out volume under a device that is otherwise present is common and frequently recovers in full. Erase means what it says. First Aid is a repair tool, and running a repair tool on hardware that has started making a new noise is the worst possible use of the time it has left. Before concluding anything, rule out the dullest cause of all: an NTFS volume will not mount natively on macOS, and an APFS or HFS+ volume is unreadable to Windows without extra software. Plenty of drives declared dead are only plugged into the wrong operating system.
Four things mark the boundary, and any one of them is enough. A noise the drive did not make a month ago, particularly after a knock or a fall. A volume reported as RAW that holds anything you would be sorry to lose. Detection that is getting worse week by week. Or recovery software that ran overnight and produced a folder full of files that will not open. Past that line, carrying on is not a neutral act — it consumes exactly the working life a proper recovery needs.
What follows is deliberately dull. If the bare drive slides out without force, send that on its own; if it does not, send the whole unit with its power supply. Pack it so nothing can move inside the box, and post it tracked and insured to Guildford Data Recovery, Building 2, Ground Floor, Guildford Business Park, Guildford, GU2 8XH. That is about eighteen miles from Bracknell, roughly forty minutes down the A322 and then the A3, and reception takes devices over the counter Mon–Fri 9:00am–5:30pm if you would rather hand it over in person. Nobody collects — there is no van and no Bracknell counter — so posting it is genuinely the quickest route. Two working days after it is booked in you are told which of the three hurdles it was failing, what will realistically come back, and the price in writing: £300 + VAT covers a single hard drive or an SSD, NVMe at the same rate. Decline it and you are out the cost of return postage, nothing else. For anything you want to ask first, the freephone is 0800 689 0668, Mon–Fri 9:00am–5:30pm.
A drive that needs three attempts to appear today will need thirty next week. Intermittent detection is not a quirk to be worked around; it is a countdown with a fixed number left on it. Spend the remaining mounts copying files off, not proving to yourself that it still works.
Free diagnostic closing 2 working days after your device is booked in, one fixed written quote, and no fix, no fee on logical faults. Cards and USB sticks £250 + VAT, any single drive or SSD £300 + VAT.