If Time Machine can't use your backup disk to back up or restore your files, try these solutions.
If your Mac doesn’t start up all the way, resolve that issue first.
Make sure that your backup disk is supported by Time Machine.
If Time Machine says that your backup disk doesn't have enough storage space or is nearly full, use a backup disk that has at least twice the storage capacity of your Mac. For example, if your Mac has 1TB of storage, your backup disk should ideally have at least 2TB of storage. If necessary, you can choose items to exclude from your backup.
Check the connection to your backup disk.
If your backup disk is connected to your Mac, make sure that it's connected directly to your Mac, not through a USB hub or other device.
If your backup disk is connected over your local network, make sure that the network connection is good and your Mac is connected to the same network as the backup disk. If you completed a previous network backup successfully, you can verify that backup: Press and hold the Option key while choosing Verify Backups from the Time Machine menu in the menu bar.
If you're also using a cloud-based syncing or backup service, Time Machine might say that some of the files on your Mac cannot be backed up until syncing is completed. To ensure that syncing can complete promptly, keep your Mac plugged into power and connected to the internet. If you don't want to wait for syncing to complete, you can temporarily exclude your sync folders from the Time Machine backup.
If Time Machine reports that the backup is delayed or could not be completed because some files were unavailable, complete a manual backup while your Mac is unlocked, or wait for Time Machine to try again during future automatic backups. (Certain protected files might require that your Mac be unlocked before Time Machine can access them.)
Check for VPN software or other third-party security software, which can affect the connection to your backup disk.
Make sure that the firmware of your backup disk is up to date. Check with the manufacturer of the backup disk for details.
If you’re attempting to restore from a backup that was created in macOS Monterey 12 or later, make sure that your Mac is using macOS Big Sur 11 or later.
If no other solutions work, start over: Erase your backup disk, then use Time Machine to select it as your backup disk. Or try a different backup disk.
Learn what to do if Time Machine is working but takes a long time to back up.
Tell us more about what's happening, and we’ll suggest what you can do next.