Windows has taken a look at the volume, and could not understand the structure describing the volume. So Windows offered the only thing it knows how to do in such cases – write another one. Your files are most likely still on your disk. Only the few kilobytes that describe where they are were damaged.
"Access is denied" means it's a permissions issue. "The parameter is incorrect" means your file system is damaged. "Not formatted" means your partition structure is missing. There are three types of errors here, but none are asking to be reformatted.
Windows told you it cannot read a description of the volume. It is not telling you the drive is empty.
"You need to format the disk before you can use it" seems like good advice. In fact, it's closer to admitting that Windows tried to read the structure that describes this volume and couldn't. Therefore, all it knows how to do now is write a new one.
It's likely your files are all still in place. The small amount of information used to tell the computer how to find them — the partition table at the beginning of each disk, or the boot sector at the start of the volume — is damaged. Between them these take up only a few kilobytes of space on a drive that could contain terabytes.
Click Format and Windows will overwrite the damaged file structure with empty structures. Although the physical presence of the data still exists, what is lost is the description of where the files were located on the disk, and now, there are descriptions of an empty disk. In many cases, these can be recovered. However, recovery is materially harder — usually as "carved" files without labels (names) and without directories (folders).
The specific wording narrows down the possible causes greatly, so take note of which message you see.
Windows has located the partition, but the file system that lives within it cannot be identified. This is most frequently due to damage to the boot sector — and many file systems make copies of the file system metadata somewhere else on the volume for just such an eventuality.
This is shown in Disk Management. It signifies that the initial part of your disk's storage area is missing, i.e., the partition table. Your drive’s total capacity is usually reported correctly. This indicates your drive is communicating with Windows properly.
It is an indication of the same issue as above but indicated through a different utility. The structure of the drive is damaged but all files remain intact.
Often times it is permission issues rather than damage to the data, especially if the drive was previously used or accessed on another machine. Check the ownership of the drive before jumping to conclusions regarding corruption.
None of these include clicking the button.
Do not use Format. Do not Repair. Do not Initialize. Cancel and unplug. Each of those actions will write to the disk.
What was said? Which tool did you see it in? That information narrows down what might be wrong before even opening anything, and that is always the first question we ask when someone calls us.
If the error message states "access denied" as opposed to format issues; then take ownership of your volume. This doesn't cost anything and may completely resolve the issue.
chkdsk will make the file system consistent by removing items that are unable to be resolved – which on a damaged volume equates to deleting the record(s), or the information that a recovery tool would use to rebuild them.
Read-only recovery tools, run against an intact drive, are able to successfully reconstruct a partition table. The recovery tool should be installed on another disk drive and the files recovered to yet another disk.
The reconstruction depends on the fact that file systems announce themselves.
All file systems write a unique boot sector or superblock signature at the beginning of each volume – NTFS, exFAT, FAT32, APFS, HFS+, ext all have distinctive boot sectors or superblocks. Scanning for those signatures in an image of a drive locates the start point of each volume regardless of what is missing from the original table.
The volume size is determined using records in the file system itself, and then a corrected partition structure is rebuilt within the image. Where the boot sector is damaged, most file systems keep a backup copy of it – NTFS at the end of the volume, ext in its superblock copies – and this is used to rebuild the volume instead.
This whole process takes place against a read-only image so it will never alter the original. That is the difference between this methodology and clicking Format: one rebuilds the map whilst the other completely replaces it. Single drives in Manchester are available from £300 +VAT after a free 48-hour diagnostic. These usually fall into the quicker recoveries when the hardware is sound.
No. That message does not mean your disk is empty. It means Windows can't interpret how you have organised your files. Formatting would overwrite the damaged file system with an empty one. All of your physical files will still exist on the disk. They simply won't have their corresponding records showing where they reside.
Not immediately. However, this will make recovery very difficult. While all of your files will continue to exist as a physical entity on the hard disk, when you recover them after having formatted, the recovered files will typically appear without names, and will not retain their original folder structure. On a computer containing mostly documents, recovering all those files with no folders is a much worse outcome.
This is structural damage to approximately a few thousand bytes describing the volume itself — for example, a partition table at the beginning of each disk or a boot sector at the beginning of each volume. It commonly occurs as a result of a bad interruption during a write operation, being disconnected from power while writing to the disk, being unplugged in mid-write operation, or a bad area appearing in the affected portion of the disk.
Related but not identical. Not initialized means the partition table is gone; needing to format means a found partition's file system cannot be read. Both are structural damage with the data intact underneath and both offers should be declined.
In some cases where the mechanical portion of the hard drive remains intact, read-only recovery utilities may be able to build a new partition table from identified file systems based on file system signature recognition. The software should be installed to another drive or disk, with all recovered files placed on a third device. If you hear any noises coming from the original drive, do not continue.
Yes, if the original data structures are simply rebuilt instead of being "carved" out from the original location, the volume will mount in the same way it did before. This is only true when the original structures exist, which is exactly what clicking “Format” destroys.