AndyKirby wrote:
MacBook Pro 2018 was running fine - left the room for a moment - when I came back it was sat with the black screen and the folder with a question mark indicating it can’t find a boot volume.
The SSD may have died. Most SSD failures occur suddenly.
next idea was to get a friend to make me a bootable usb stick. This is recognised and I can start to boot but again at about 2% progress it restarts the macbook
Unless you previously adjusted the Mac's security settings to allow for booting from USB, then this will not work now since the only way to change the security settings is from Recovery Mode. If you attempt to boot from USB when the security settings have not been adjusted to allow for booting from USB, then it will boot into Recovery Mode to tell you about it.
About Startup Security Utility on a Mac with the Apple T2 Security Chip - Apple Support
final thing - I tried the diagnostics - which download from the internet and does run successfully finishing with ref code ADP000 (no issues found)
so hardware is ok…
No, that is not what a passing diagnostic means. A passing diagnostic only means that no issues were detected at the time of the scan. I've run diagnostics in loop mode and errors will either show up in the first pass, or they won't show up until after a 100 passes. In fact the only useful diagnostic is one which produces an error or one which freezes the system during testing.
but won’t start recovery, internal drive not recognised as bootable and won’t boot from bootable usb.
what should I try next?
The only thing left is to try to "Revive" it, but more than likely you will need to resort to a "Restore" of the firmware which will reset the T2 security chip as well as pushing a clean OS to the internal SSD. A "Revive" should not affect any data on the SSD, but a "Restore" will destroy all data on the internal SSD.
Revive or restore an Intel-based Mac using Apple Configurator - Apple Support
If a "Restore" is not successful, then the only option left is to have Apple or an Apple Authorized Service Provider examine the laptop to provide you with a repair estimate.
I hope you have a good backup of this laptop because it is doubtful any data will be able to be recovered. You can check with a professional data recovery service such as Drive Savers. They provide free estimates and are also recommended by Apple and other OEMs.