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Essential Data Recovery

External drive detected but not accessible

The parameter is incorrect, access denied, corrupted and unreadable: what each means, the safe checks first, and why the repair-first order is what loses data.

Written by Essential Data RecoveryPublished 2026-09-12Safety-critical: owner-reviewedRevision 1
A closed external hard drive beside a folded paper note on a pale oak desk in morning window light

Do not format, do not initialise, do not run DiskPart, and do not let a repair tool fix the drive yet. Windows' most convenient offers in this situation are also the destructive ones. The data on a drive like this usually survives; the fixes are what end it.[1]

A drive that appears in Windows but refuses to open is usually a file system or permission problem, not a dead drive. The messages, 'the parameter is incorrect', 'access is denied', 'corrupted and unreadable', or an offer to format, all mean Windows cannot read the drive's bookkeeping normally. The data is very often still there, and the order of operations decides whether it stays that way: copy or recover first, repair later if ever.

This guide covers an external or USB drive that Windows can see in File Explorer or Disk Management but will not open normally. It does not cover a drive that does not appear anywhere, a drive making new noises, or Mac-side permission questions; each of those is a different situation.

Not sure which situation you are in? Guided help walks you through it.

What each message is telling you

'The parameter is incorrect'

This one usually points at file system damage rather than dead hardware. There is no official Microsoft definition attached to the drive-access form of this error, so be wary of confident explanations online; the practical reading, that the file system is not answering normally, is consistent with how it behaves. The correct response is not to fix it in place but to get the data off or recovered first.

'Access is denied'

This is the recoverable kind: an ownership and permissions problem, often after the drive was used with another computer. Microsoft's takeown command exists precisely to recover access by becoming the owner of files. Change ownership only after copying what you can, because permission changes write to the volume, and on a drive with deeper problems every write counts.[2]

'Corrupted and unreadable' or an offer to format

File system corruption is the common thread. NTFS is designed to absorb some of it: Microsoft documents its transaction log restoring consistency after failures and bad sectors being remapped. When damage exceeds what the file system can heal, Windows stops offering the drive and starts offering to format it. That prompt is a symptom, not a solution; the RAW drive guide covers it in detail.[3]

Windows shows the drive as RAW or keeps asking to format: what to do first.

Check the boring causes first

Cheap checks that rule out half the causes

  1. Use a different USB port directly on the computer, not a hub. Microsoft notes USB disks sometimes draw more power than some ports supply, hubs especially.
  2. Try a different data cable; cables fail quietly and often.
  3. Try a different computer. If the drive misbehaves everywhere, the drive is the suspect; if it works elsewhere, your PC is.
  4. Open Disk Management and read the status column. A drive shown as RAW or Unallocated points at the file system; Microsoft's documentation treats a Failed status or repeated failure to initialise as a sign the disk itself is failing.
[4][5]

Why repair-first loses data

The tools Windows offers here are safe on healthy drives and destructive on damaged ones. chkdsk changes nothing until run with its fix options, and then it repairs the volume's structure: on FAT file systems Microsoft documents that these repairs usually change the allocation table and sometimes lose data, and on drives with failing hardware Microsoft says chkdsk can behave unpredictably while its thorough /r pass reads every sector. Formatting, offered in the same dialog, is a quick format by default and erases the file system; initialising a disk erases all data on it, by Microsoft's own warning; and DiskPart clean removes all partition information with no confirmation, a lack Seagate's guide makes a point of warning about. Every one of these is a step for after the data is safe.[6][7][1][8][9]

The recovery-first order

If some files are still visible

  1. Copy what opens normally to another drive straight away; a partially working drive is still a working source for the files that read.
  2. For files that will not open, or a drive that opens not at all, run one recovery scan: tools such as PhotoRec are documented to read the drive without writing to it, and TestDisk can repair partition structures when that is the specific problem.
  3. Save recovered files to a different drive, never the affected one.
  4. Only once everything is safe should you consider repairs, formats or DiskPart, and then only to prepare the drive for reuse.
[10][11]

When the drive itself is failing

Sometimes inaccessibility is the first public symptom of hardware failure: Microsoft names a failing disk as the most common reason a disk will not initialise, and treats Failed status as indicating data loss unless repaired. If the drive also clicks, grinds, or drops off the bus mid-read, stop connecting it repeatedly and read the clicking guide; if it has vanished from the system entirely, the not-detected guide covers that case. Where the data matters, Microsoft's own documentation notes that a data recovery lab is the remaining option.[5]

Clicking hard drive: what to do, and what never to do.

Choosing a data recovery service: quotes, privacy and honest guarantees.

Sources

Facts on this page are cited to the publishers’ own documentation.

  1. [1] Microsoft — clean (Windows command reference). captured 2026-09-12.
  2. [2] Microsoft — takeown (Windows command reference). captured 2026-09-12.
  3. [3] Microsoft — NTFS overview. captured 2026-09-12.
  4. [4] Seagate — USB external troubleshooter. captured 2026-09-12.
  5. [5] Microsoft — Troubleshoot Disk Management. captured 2026-09-12.
  6. [6] Microsoft — Format-Volume (PowerShell storage module). captured 2026-09-12.
  7. [7] Microsoft — Initialize new disks. captured 2026-09-12.
  8. [8] Microsoft — chkdsk (Windows command reference). captured 2026-09-12.
  9. [9] Seagate — How to DiskPart erase/clean a drive through the command prompt. captured 2026-09-12.
  10. [10] CGSecurity — TestDisk. captured 2026-09-12.
  11. [11] CGSecurity — PhotoRec. captured 2026-09-12.