You put a card in the reader and nothing happens. No icon on the desktop, no ingest, no sound. Before you reach for Erase, remember that the card may be the only copy of the shoot. Formatting is the last step, not the first. Here are seven checks, in the order that wastes the least time.
- Look in the right place. A mounted card can be hidden. In Finder, open Settings (Preferences before macOS 13) and tick External disks under both General and Sidebar. Then look in the sidebar rather than on the desktop.
- Swap the easy parts. Reseat the card, then try another USB port, another cable, another reader. Plug the reader directly into the Mac instead of a hub or a monitor's port. A flaky reader or hub causes more "dead cards" than dead cards do.
- Check the lock switch. On a full-size SD card, a small slider on the side marks the card read-only. If it has slipped down, flip it back up and reinsert. A card in that state can behave oddly even when it appears.
- Ask Disk Utility. Open it, then choose View > Show All Devices. If the card is listed but greyed out, its volume isn't mounted: select the volume and click Mount. If it isn't listed at all, the Mac isn't seeing the card, which points back to the reader, the port or the card itself.
- Run First Aid. Apple's instructions: with all devices shown, run First Aid on each volume, then on the container, then on the device itself. It repairs file system errors left by a camera that lost power or a card pulled mid-write.
- Don't click Initialize. If macOS says the disk isn't readable, the dialog offers Initialize, Ignore and Eject. Initialize erases the card. Choose Ignore and move to the next step.
- Try another computer. If a second machine, or a different operating system, reads the card, copy everything off it first and sort the problem out afterwards.
If it still won't read: stop writing to the card and put it aside. Apple's own advice when First Aid can't repair a disk is to back up as much as you can before reformatting it. For a camera card, that means data recovery software, run on a copy of the card if the tool allows it. Free open-source tools such as PhotoRec exist, as do paid ones. Format the card only after you have the files, and then format it in the camera.
Why a card that "worked yesterday" stops mounting
The usual causes are boring. The camera lost power or the card was pulled while it was writing, so the file system was left half-updated. The reader is worn. The card was moved between cameras of different brands. Or the card is simply failing. Cards that fail once tend to fail again, so once you have rescued the footage, retire the card from important jobs.
When the card does mount, copy first
A card that has just misbehaved is the card you should copy from before doing anything else, and copy with a check at the end, not just a drag in Finder. A verified copy reads every written file back and compares it with the source, so you know the files are intact before the card is wiped. Our guide to checksum verification shows what that check does.
ShotGrab can only work with cards macOS has mounted. It doesn't repair a card or bypass the file system, so if the checks above fail, the fix happens before ShotGrab, not inside it. If the card does appear, ShotGrab copies and verifies it automatically when the project is armed, and it never writes to the card, with one optional exception: the reversible "mark for formatting" step, which you choose yourself. And if you ejected a card from ShotGrab's Disks sidebar earlier, it only disappears from the Finder: it stays in the sidebar greyed out, and you can reactivate it from the right-click menu.
What we couldn't confirm
Apple's Disk Utility guide covers First Aid and the Show All Devices view, but we did not find an Apple page that lists every reason a memory card fails to mount. The other checks come from common practice and from support articles of third-party repair tools, so treat the order as a sensible default, not as an official procedure.