Reinstalling does not clear a disk by design. What is left afterwards depends on the option that was chosen, on whether a format happened on the way through, and on whether the storage is mechanical or flash. This page goes through all six variations, names the two where the truthful answer is that nothing can be done, and explains why the machine should be switched off rather than searched.
One disk is £300 + VAT, and establishing what is left costs you nothing. After a reinstall the free diagnostic is the most valuable half hour in the process, because it decides whether there is any work to buy before you have spent a penny.
Putting Windows back on a machine does not wipe it as a matter of course. How much is left turns on three things: the button that was pressed, whether a format happened along the way, and what sort of disk is underneath. Find your version below.
The mildest of them. Windows sets your personal folders aside, lays down a new system and returns them afterwards, so in most cases nothing has actually gone anywhere. Check the user folder, then check for a directory called Windows.old at the top of the drive. A great many of these need no laboratory whatsoever.
Here the type of disk decides the outcome entirely. Spinning platters keep their contents when space is released, so a machine stopped promptly usually gives back a great deal. Flash storage does not work that way, because the controller clears released blocks by itself, and it does so long before anybody has finished panicking.
The installer lays a new system down and does not set out to erase anything. Call it twenty to thirty gigabytes of writing, so that much of what was there has gone and the remainder may be perfectly readable. What comes back is whatever the fresh installation happened not to sit on top of.
Setup uses the fast kind of format, which swaps the index and leaves the contents in place, so this is a harder job rather than a hopeless one. The number that matters most is not the format at all — it is how many hours the machine has been used since it came back up.
Two drives in the machine, the installer numbered them differently from Windows, and the new system landed on the one holding the data. Turn it off now. Do not attempt to put it right by installing again in the correct place, because that simply repeats the damage in a second location.
People assume calamity and are usually wrong. Where the files sat on a separate internal disk or an external unit, the installer never went near them. What tends to have disappeared is a drive letter or a set of permissions, and neither of those is damage.
Ask most people what a reinstall does to a disk and they will say it clears it. It does not. Setup writes an operating system into part of the available space and flags the rest as usable, and those are two very different operations. Your old material is still lying in every region the installer did not reach, and it stays legible for exactly as long as nothing new is placed on top of it.
Hence the hurry. A newly installed Windows is anything but idle: it fetches updates, indexes the disk, generates restore points, unpacks drivers and writes logs, hour after hour, and all of that activity is directed into the space now considered spare — which is precisely where your documents are. A machine left switched on for a fortnight after the event returns a fraction of what one stopped inside the hour returns.
Where a reinstall went over the top of an existing system without a format, the previous installation and your entire profile are usually parked in a folder called Windows.old in the root of the drive. Documents, pictures, the desktop, downloads — often sitting there whole, needing nothing more sophisticated than a copy and paste.
Two things take it away. Windows removes it by itself after roughly ten days, and the disk cleanup tool offers to delete previous installations, which people accept while hunting for free space. If that folder exists, empty it into somewhere safe this evening rather than at the weekend.
This deserves bluntness rather than diplomacy. A mechanical disk keeps whatever is in a freed area until something else is put there, which is the whole reason recovery after a reinstall works so often. Solid state storage behaves differently: releasing space notifies the drive, and its controller then wipes those blocks in its own time so they are ready to accept new writes. It happens quickly, it happens without the computer's involvement, and no laboratory anywhere can reverse it.
The upshot: a remove-everything reset on flash storage, or a format of one, typically yields zeros. Where the machine was shut down the instant the mistake was noticed there may be a slim chance, and the diagnostic costs nothing, so it is worth asking. Where it has been in daily service for a month, a straight no on the telephone saves you the postage.
Software. Your material comes back — letters, spreadsheets, pictures, mailboxes, project directories, databases, saved games — but applications are not files sitting in a folder. They are entries in the registry and components scattered through system directories, all of which the new installation replaced, so every one of them has to be put on again from its installer. Product keys written down in a document or sitting in an old email come back like any other file, which is usually the real worry behind the question.
Beyond that, anything the new system physically wrote over is gone, and no technique reaches it. That is the whole reason the first instruction on this page is to stop using the machine.
Shut it down properly and resist restarting it for another look. Booting writes.
Do not put recovery software onto the disk you are hoping to recover. It is a genuinely common own goal, because the installer deposits itself into exactly the free space holding the missing material. If software is going to be tried at all, run it from a different computer with the affected disk attached as a secondary drive.
Then get the disk out and send it, or hand the machine to somebody who can extract it. Nothing is taken apart at this end, and a bare drive is what the bench works with. Where the storage is soldered to the mainboard — Apple Silicon machines and a few very slim laptops — it cannot be removed, cannot be posted, and cannot be helped by anybody.
A copy is taken first and everything afterwards happens against that copy. The wreckage of the previous file system is then pieced together, and old directory records very often survive in areas the new installation never touched, which is what allows folder trees and proper file names to reappear rather than a shapeless pile of documents. Where those records have gone, material is identified by its own contents and returned intact under new names.
A list of what has been found goes to you before anything is handed over, so you can measure it against what you were hoping for. On this kind of job that list is the honest answer, because a reinstall recovery is almost never all or nothing.
One hard drive or SSD: £300 + VAT, fixed in writing after a diagnostic that costs nothing and closes two working days after the disk is booked in. Cards and USB sticks: £250 + VAT. Recorder disks and encrypted volumes where the key can be supplied: £400 + VAT. Arrays, NAS units and servers: from £500 + VAT, rising with the number of members. Forensic work: £800 + VAT with a full written report, or £400 + VAT for a binary image with deleted-file extraction and no report.
A reinstall over a mechanically sound disk is a logical job, which means the no fix, no fee guarantee applies and an empty-handed result costs you nothing. The listed exclusions are electronic failure, mechanical failure, chip-level work, DVR jobs and forensic jobs, and physical work is billed 50 per cent in advance. Jobs of this type are frequently finished two to four working days after they are authorised.
Post it tracked and insured, or bring it in: Compass House, Vision Park, Chivers Way, Cambridge CB24 9AD, drop-offs Mon–Fri 9:00am–5:30pm. About 70 miles from Leicester, the M1 to J19 and then the A14 east, roughly ninety minutes, two minutes off Junction 32 with parking outside the door. Nobody collects and there is no counter in Leicester.
A good share of these arrive from students at the two universities and De Montfort in the weeks before a hand-in, and from people who took a slow laptop somewhere to be sorted out and were handed back something spotless. Neither is a daft position to be in, and both are far easier to put right on day one than in week three.
A brand new Windows writes to the disk almost continuously, and all of it lands in the area holding what you are trying to get back.
Cards, sticks and single drives are the easiest things in the world to post, and posting them is gentler than a day of being carried around in a coat pocket. A padded envelope handed over in Leicester tends to reach the Cambridge bench the next working day.
The general rule is the drive travels and the machine stays behind — out of the laptop, out of the tower, out of the iMac, out of the recorder under the counter. This bench does not dismantle equipment, and a repair shop will do it while you wait. Three things are the other way round, and getting them wrong costs you the recovery: an external drive stays sealed in its own case, a NAS comes as a complete unit, and a WD My Passport or My Book travels whole with its cable, because on those the encryption key is held on the bridge board rather than on the disk — separate the two and the data becomes unreadable even to us. A Fusion Mac needs both of its drives, each labelled. The one thing nobody can work round is flash soldered onto the mainboard, as on Apple Silicon machines: if it will not come off, there is nothing to post.
↓ Print the shipping & booking-in form (PDF)
Address it to Cambridge Data Recovery. It is about seventy miles from Leicester if you fancy driving it — M1 south to Junction 19, then the A14 east — and the lab is two minutes off Junction 32 with parking at the door. Posting costs you a stamp and a day instead. Whichever you choose, you hear from us the moment it is booked in, and the free diagnostic closes two working days after that.
Not certain what belongs in the box? Ring 0800 689 0668 before you tape it up, or let the free online diagnostic ask the questions for you.