You pressed the power button, the screen lit up — and instead of the Apple logo you got a gray or black screen with a circle and a diagonal line through it. Apple calls this the prohibitory symbol. It looks alarming, but it has a very specific meaning, and in most cases you can fix it yourself in under an hour without losing any files.
What the circle with a line through it means
The prohibitory symbol means your Mac found a startup disk, but the copy of macOS on it can't be used. That's different from the flashing folder with a question mark (no startup disk found at all) and different from being stuck on the Apple logo (macOS starts loading, then hangs).
The usual causes, roughly in order of how often we see them on trade-in benches:
- An incompatible macOS version. The disk has a build of macOS that's too old or too new for this specific Mac — common after swapping drives between Macs, restoring from another Mac's backup, or a botched downgrade.
- A macOS update that didn't finish. Power loss or a forced shutdown mid-update can leave the system half-written.
- Disk corruption. The system files macOS needs at boot are damaged.
- Booting from a blocked external drive. Intel Macs with the T2 chip block external boot by default, and show this symbol when you try.
Step 1: Rule out the simple stuff
Unplug everything — external drives, hubs, SD cards. If your Mac was trying to start from an external disk, removing it may be the whole fix. Then force a restart: hold the power button for about 10 seconds until the Mac turns off, wait a few seconds, and press it again.
Step 2: Boot into macOS Recovery
- Apple silicon (M1 and later): hold the power button until you see "Loading startup options," then click Options → Continue.
- Intel: press the power button, then immediately hold Command-R until the Apple logo or a spinning globe appears.
Recovery lives on a separate hidden partition, so it usually loads even when the main system won't.
Step 3: Run First Aid in Disk Utility
In the Recovery window, open Disk Utility, select your startup disk (usually "Macintosh HD"), and click First Aid. This repairs the directory damage that most often causes the symbol. If First Aid reports errors it fixed, restart and see if the Mac boots normally.
Step 4: Intel Macs with a T2 chip — check Startup Security Utility
If the symbol appears only when you boot from an external drive on a 2018–2020 Intel MacBook, it's the T2 chip doing its job. In Recovery, go to Utilities → Startup Security Utility and set "Allowed Boot Media" to allow external drives. Skip this step if you're booting from the internal disk.
Step 5: Reinstall macOS
If First Aid didn't fix it, go back to the Recovery main window and choose Reinstall macOS. This replaces the operating system without touching your personal files. On Intel Macs you can also try Option-Command-R at startup, which installs the newest macOS your model officially supports — the cleanest way out of a version mismatch.
If the installer refuses because "macOS could not be installed on your computer," the version on the disk is incompatible with your hardware. Erasing the disk in Disk Utility (back up first if you can mount it on another Mac) and reinstalling from Recovery clears that.
If nothing works: it may be the drive, not the software
A Mac that shows the prohibitory symbol again within days, or an SSD that First Aid can't even see, is usually failing hardware. On 2016-and-later MacBooks the SSD is soldered to the logic board, so the repair is a board-level job that often costs more than the Mac is worth.
Two honest options at that point: we buy Macs that won't boot — a prohibitory-symbol Mac still has real trade-in value because the screen, case, and battery are fine — or you can put that credit toward a working replacement from our Apple clearance lineup, where every Mac ships free with a 1-year warranty.
Frequently asked questions
Is the prohibitory symbol the same as the flashing question mark folder?
No. The question-mark folder means no startup disk was found. The circle with a line means a disk was found but its macOS can't be used on this Mac. The fixes overlap (Recovery, Disk Utility, reinstall), but the causes are different.
Does the circle with a line mean my files are gone?
Usually not. The symbol is about the operating system, not your data. Reinstalling macOS from Recovery preserves your files. If Disk Utility can't mount the disk at all, stop and get the data professionally recovered before erasing anything.
Why did this appear right after a macOS update?
The update likely didn't finish writing system files — a forced shutdown or power loss mid-update is the classic trigger. Reinstalling macOS from Recovery re-writes the system cleanly and normally resolves it.
My Mac shows it only when booting from a USB drive. Why?
Either the external drive's macOS is incompatible with your Mac, or (on T2-equipped Intel MacBooks) external boot is blocked by default — see Step 4.
Should I check for this when buying a used MacBook?
Yes — always watch a used Mac boot fully to the desktop before paying. A seller who will only show you the Mac powered off may be hiding a boot problem. Every refurbished Mac we sell boots, passes diagnostics, and carries a 1-year warranty.