This pop-up is the single biggest data-loss trap with SanDisk sticks. Windows shows it when it cannot read the file system, and the wording nudges you straight toward the button that erases your chances. The drive is usually not blank. The index that points to your files is just unreadable, which is exactly what a recovery scan rebuilds.

Honestly, the most common mistake we see is people formatting before they have copied a single file off the stick, because the dialog made it feel like the only option. Close it, run the recovery walkthrough above, and only format once your recovered files are sitting on a different drive. SanDisk's own help pages on the format error say the same thing: recover first, format second.

A RAW drive looks empty or prompts for a format, and Disk Management lists it as RAW instead of FAT32, exFAT, or NTFS. People reach for chkdsk and hit a wall, because chkdsk repairs an existing file system. It cannot fix one that is gone. Microsoft's own community answers confirm the tool simply will not run on a RAW volume.

The order that works: recover your files first with recovery software, which reads the raw sectors directly and does not care that the file system is missing. Then, with your data safe, reformat the stick (exFAT for a USB drive used across devices) to lay down a fresh file system. Our guide to SD card recovery walks through the same RAW-then-reformat flow for memory cards.

Write protection shows up as "the disk is write-protected" when you try to copy, delete, or format. Start with cheap fixes. Some adapters and a few full-size SanDisk sticks have a tiny lock switch. Slide it off. If there is no switch, open Command Prompt and clear the read-only attribute with diskpart.
diskpartlist diskselect disk X
attributes disk clear readonly
Replace X with the SanDisk disk number from list disk. Get this wrong and the command hits the wrong drive. If diskpart reports success but the stick is still locked, try the StorageDevicePolicies registry value. Users on SanDisk's own forums walk through the same escalation for a write-protected drive.

Here is the part the quick-fix articles skip. When none of the software tricks work, the write protection is not a Windows setting. It is the flash controller switching to read-only as a last-ditch protection because its memory is wearing out. A long Tom's Hardware forum thread documents drive after drive where this lock is permanent and no utility removes it.

That sounds like bad news, and for the drive it is. For your files it is the opposite. A read-only stick still mounts and still reads, so this is your window to copy the data off, manually or with a recovery scan, before the controller fails completely. Treat the first write-protect error as a warning light, not a puzzle to beat.

"Not recognized" covers a range, so narrow it down. If the drive shows in Disk Management but has no letter, assign one or it may be RAW (see above). If it shows as "No Media" with zero size, the controller has usually failed. If nothing appears at all, swap the port and cable, then try another computer. A surprising number of "dead" sticks are really just dead front-panel USB header.
Picture the interview folder you needed by Monday morning sitting on a stick that will not mount. The instinct is to keep replugging it, but repeated power cycles stress a dying drive. Test it once on a second PC, and if it still will not appear, stop. More attempts only lower a recovery lab's odds. Our USB recovery walkthrough covers the same detection checks for other brands.

When the SanDisk drive still mounts but throws read errors or odd file behavior, chkdsk and the Windows Error Checking button (drive Properties, Tools tab) can repair the file system. Open an admin Command Prompt and run it against the drive letter.
chkdsk X: /f

The /f flag fixes file-system errors; adding /r also hunts bad sectors but takes much longer. The catch, spelled out in Microsoft's chkdsk reference: it moves and rewrites data while it works, which a healthy drive shrugs off but a failing one may not survive. That is why recovery comes first and chkdsk second.

Capacity loss has two very different causes. The honest one: a partition or a failed format left the drive showing a fraction of its size. In Command Prompt, diskpart clean wipes the partition table so you can create a fresh full-size partition. This erases the drive, so recover anything you need first. Microsoft's community has a clear walkthrough for restoring full capacity with diskpart.

The dishonest one: a counterfeit drive flashed to report 256 GB while holding 32 GB of real memory. No tool fixes that, because the storage does not exist. Writing past the real limit silently corrupts files. A capacity-test utility like h2testw tells the two cases apart before you trust the stick again.

Chasing firmware is the most common dead end in the whole search. People look for a "SanDisk USB firmware update tool" expecting an official fix, but SanDisk's Dashboard utility manages SanDisk and WD SSDs. It does not list USB flash drives at all.
What is left are MPTool or "mass production" utilities, made for specific memory controllers by the chip vendors, not by SanDisk. They can sometimes revive a stick, but they reformat at the controller level and erase everything, and matching the exact controller is guesswork. Flash the wrong one and the drive is permanently bricked. For a USB stick, recovery plus a normal reformat is almost always the safer call than chasing firmware.

Searches for an "online" SanDisk repair tool are common, and it is worth being clear: a browser tab has no low-level access to a USB device plugged into your machine. The pages that rank for those terms are either ads for downloadable software or thin link farms. Anything that genuinely repairs a file system or recovers files needs direct, block-level access to the device, which only an installed program gets.

There is a privacy angle too. The files on a damaged SanDisk drive are often personal, things like photos, documents, and scans. Handing those to an unknown upload server is the real risk. Greyed out, or "processing in the cloud"? That is a reason to walk away, not to hand over your photos.

• Tom's Hardware forum Hardware-level write protection on a flash drive is often irreversible
• Microsoft Tech Community Restoring a USB drive to full capacity with diskpart
• SanDisk community forum Owner discussion of a write-protected SanDisk drive