When a computer function works in another app, user account or port, keep the repair inside the failing context. For Mac startup disk, first open Startup Options, record visible volumes and run Disk Utility First Aid from recovery.
What this covers
- Mac startup disk with this exact failure state
- Diagnosis across drive visibility versus macOS volume, encryption and boot policy
What it does not cover
Try in this order
0 of 4 completedCapture the exact failure state
ReversibleName the failing app, user account, port or peripheral and one that still works. Expected behavior: appear in Startup Options and load macOS without filesystem or hardware errors.
Isolate the component boundary
ReversibleOpen Startup Options, record visible volumes and run Disk Utility First Aid from recovery. Swap only the app, account, cable, port or user profile while keeping the computer unchanged. Boundary to separate: drive visibility versus macOS volume, encryption and boot policy.
Correct only the proven cause
ReversibleRepair supported filesystem issues or restore/replace storage after a verified backup. Repair the isolated app, user profile, driver binding or physical path.
Verify and stop safely
ReversibleRetest both contexts after sign-in and one cold restart. Stop for missing unique data, liquid, impact or repeated storage errors.
Evidence ledger
Sources behind this answer
Exact questions