Before you touch any settings, plug it in and let it sit there for a couple of minutes; listen for sounds and look for lights. Are the lights lit? Do you feel it spinning when you put your finger against the casing? Can you hear anything new coming out of it? These are all important signs, because 'not showing up' covers three very different faults: a faulty connection (which will cost you little to fix), a software glitch (fixable with some care and patience) and a physical failure inside the drive, which is a job for the lab.
If your external drive is clicking, buzzing, beeping or constantly spinning up and down, stop immediately. Mechanical sounds like these usually indicate a failure of either the read/write heads or the motor, and are far more likely if the unit has been dropped or knocked. Any additional power applied to the unit risks further damage to the platters where your files reside. Shut off the power and go directly to the last part of this guide.
Swap the USB lead first: the cheap ones included with portable units break far too often, and Seagate and WD models seem particularly prone to it. Next, swap ports: connect straight to the computer (not through a hub or the front-panel sockets) and, if possible, run your tests on a completely separate computer. Desktop units need a working power brick for the disk to operate, so if the disk won't spin at all, try a known-good adapter before assuming disaster.
On Windows, right-click the Start button and go to Disk Management. A drive showing up in Disk Management but not in File Explorer is probably just missing a drive letter: right-click the partition and select 'Change Drive Letter and Paths' to assign one. If the drive says RAW, says it's unallocated or wants to be initialised, then the partition or file system is corrupt. Your files are almost certainly intact; however, do not initialise, format or agree to Windows' prompt to fix it, as each of those writes over exactly the structures a recovery rebuilds from.
When using a Mac, open Disk Utility and choose "View > Show All Devices". If you see your hard drive physically listed but the volume won't mount, don't erase it (that wipes everything on it) and be cautious about running First Aid on a drive that sounds like it's struggling, because repair functions force the drive to work even harder than it already is. Also, when an external drive mounts perfectly well under Windows yet refuses to mount under Mac (or vice versa), there usually isn't anything wrong with the data. It is probably just formatted for the other platform, so read it on the system it was created on.
If your Seagate external drive's light comes on but you still cannot find it anywhere, and it is not making any strange noises, it is probably due to a fault in the USB bridge board or its firmware. Both problems are recoverable, but certainly not by buying a different cable. And although some people might be tempted to remove the outer casing of their WD My Passport and Elements drive and attach the bare drive inside directly, please don't bother on most current units. Modern WD Passport and Elements drives use hardware encryption, meaning the USB circuitry itself encrypts all of your data, so a drive attached without its USB board shows nothing but gibberish. A lab reads it properly by working with or around that original bridge.
Either way, do not continue to try connecting it just to see if it returns. Detection that becomes less frequent over time is a failure curve, not a state of mind, with each successive attempt to connect it representing another rotation of an already failing piece of equipment.
Stop straight away if the drive makes a clicking or beeping noise, or has been dropped; if Windows identifies it as "RAW" or "uninitialised" and your files are important; if detection is becoming progressively unreliable; or if you've spent hours running data recovery software with no results. At this point the maths is simple: each additional DIY attempt puts your data at risk, and having us diagnose exactly what is wrong costs you nothing.
Call us on 0800 689 0668 to get a quote first, then post the complete external drive in its enclosure with its cable and any power supply (bubble wrap will suffice). Within two working days of it arriving at our laboratory, you'll receive a diagnosis identifying what data can be recovered, along with a single fixed price, and in most cases you only pay if we recover your data. For further information see external hard drive recovery, or start with the free online diagnostic to get your quote before posting your device.
The golden rule: if your data matters and your drive is making any sound it never used to make (clicking, buzzing, beeping), cut the power now. Mechanical faults only ever get worse the longer the drive runs.
Free diagnostic, fixed quote, and in most cases you only pay if we recover your data. Start now or call the freephone.