Lighting bolt on screen appeared when there was error uploading latest version of MacOS

zix180 Said:

"I now have flashing '?' On my screen"

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Boot into Safe Mode:

Hold Down the Shift Key upon boot. Once at the login screen, release shift. See if it all now works. In Safe Mode, only necessary items load (i.e. the caches), and new preferences are set aside.

If nothing above works, then...

Reinstall the macOS:

Nothing would be lost, it's just that sometimes changes are made to your system, and then then processes become corrupted, technically. When reinstalling, deleted files are reinstalled, and misplaced files are moved back to where they should be

Reinstalling the macOS:

Go to the following link, and choose not to erase (format) your disk: How to reinstall macOS from macOS Recovery. This would be a direct fix to the partition. It mayor may not work.

Create a Bootable Installer:

You can install Mojave from a USB Flash Drive. So, if you have access to another Mac device, then create a Bootable Installer on it. Use the following link, and proceed from there as necessary: How to create a bootable installer for macOS - Apple Support

zix180 Said:

"I now have flashing '?' On my screen: Thanks for your help, but it just keeps going back to flashing '?'.: Might be time for an upgrade🙂"

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You are welcome.

Check your Hard Drive:

Perhaps it is time to upgrade. But one more thought is to check your Hard Drive.

Use First Aid in Disk Utility:

Check the health of the Hard Drive - perhaps it is going dead. If so, well, then it's time for a new Hard Drive. In disk Utility, Its sectors would be looked at and maybe reset to make it operate as it should.

A. Run First Aid in Disk Utility:

1. Open: Applications menu
2. Select: Utilities menu
3. Select: [This Hard Drive]
4. Click: the First Aid button

See if this is then accessible.

B. Try Mounting Recovery Mode:

1. Plug in: the hard drive:
2. Hold Down: command + R upon boot
3. Select: Disk Utility
4. Select: [This Hard Drive]
5. Click: Mount
6. Click: the First Aid button

See if this is then accessible.

zix180 Said:

"Lighting bolt on screen appeared when there was error uploading latest version of MacOS I've tried shutting down and restarting, I've tried holding down 'T' key when starting...nothing works! I have Apple Macbook air:"

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Try a Restart:

Restart your Mac with nothing plugged in. See if it then works.

1. Shut Down: your Mac
2. Unplug: all cables and devices from your Mac
3. Wait: 30 Seconds
4. Hold Down: nothing
5. Power on: Mac
6. See if it now works

zix180 Said:

"I now have flashing '?' On my screen: Thanks for the tips, really appreciate the info🙂"

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You are most welcome.

For Note: You ask about upgrading. If you Mac is old and obsolete, then yes, perhaps it is time for a new one.

Getting a Used Device:

If you get one that is used, then be certain the seller logs out of iCloud on it, and deauthorizes this Mac from their Apple Account through use of TV or iTunes apps. Elsewise it is useless to you. Without them logging out of iCloud on it, and disassociating it from their account, it would be useless to you.

What to Request:

Request that they you log in yourself in, prior to handing over the money. If the seller decides to disabide by those rules you've set forth, then do not proceed with the transaction. So, have the seller go here: What to do Before you Sell, Give Away, or Trade in your Mac - Apple Support