Work out what the error actually means before you act on it. Your camera or computer is telling you that the card's table of contents, the file system, can no longer be read, so nothing can be found. It isn't telling you the photos are gone: in the flash memory itself they're nearly always intact, stored one layer below the index that broke. The cruel part of the design is the one button the message offers, because pressing it starts overwriting exactly the material a recovery is rebuilt from.
A format never repairs an index; it lays a blank one over the top. A quick format takes seconds to destroy the folder tree, filenames and dates that make your photos findable. However insistent the prompt, if the pictures matter, the format can wait.
Suspect the reader before the card. Readers are cheap and die young, laptop card slots are the least reliable of the lot, and a standalone USB reader on a second computer gives the fairest verdict. On full-size cards, check the small lock slider on the edge: if it's been nudged to the locked position, it causes odd refusals, including failures to write or format.
Two outcomes should stop the testing straight away. If the card mounts but pictures appear to be missing, take it out of use immediately and shoot nothing more, because new files land on the space your old ones occupy. And if no computer sees it at all, or the capacity reads absurdly small (a 64GB card showing up as a few dozen megabytes has a crashed controller), software has nothing to offer; from there, the route is chip-level work.
Some readers reach this page the other way round: the card misbehaved, a format looked like the reset button, and the format refused to finish. There are three usual causes: the lock slider, a controller that has dropped into read-only mode as it degrades, or electronics on the way out. The read-only case is quietly the best news on this page, because a card that locks itself often does so with its entire contents still readable.
Whatever you do, don't escalate. Repeated formats, marathon chkdsk runs and repair utilities all pile more operations onto a controller that is failing precisely because operations have become hard for it. If a card in this state holds anything you'd miss, it's now a recovery case, not a repair project.
At the bench, a corrupted card is read once, every sector in order, into an image file, and the folders, filenames and video are rebuilt from that copy while the card itself stays untouched. Cards that are dead, reporting the wrong capacity or physically snapped (microSDs especially) take a different route: the NAND chip is read directly and its contents pieced back together. Both routes start with a free diagnostic, so you have the verdict and the fixed price before any decision about spending.
Posting couldn't be simpler: get a quote first, by phone on 0800 689 0668 or with the free online diagnostic, then tape the card inside a folded piece of stiff card, put it in a padded envelope and send it tracked. The details are on the memory card recovery page, or you can go straight to the free online diagnostic.
Remember this: 'card needs formatting' means the index has failed, and the photos survive it until a format, or new shooting, writes over them. Get a quote first, then send the card exactly as it is.
The diagnostic is free, the quote is fixed, and on logical faults, in most cases you only pay if we recover your data. Start online or ring the freephone.