2010 MAC PRO

The computer shuts down because it was not able to MOUINT the boot drive -- to get lots more stuff by name to finish booting up. It started a disk repair cycle, and when the was done, the disk would STILL not Mount. So it could go no further, and rather than staying powered off, It shuts down.

The conclusion is that you drive has too many errors to MOUNT successfully, even after a repair disk cycle.

You will need to at least re-install MacOS, which generally requires a disk that will Mount. So you will have to use another disk or erase the disk.

In a Mac before 2011 models, there is no ROM-resident Utilities, only the recovery partition already on the drive.

You can try:

using Recovery (command-R at startup)

Erase the drive

re-install MacOS.

Erase and reinstall macOS - Apple Support

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+1 to what Grant Bennet-Alder wrote/posted. You Mac Pro needs+ requires a good healthy ( problem-free) solid working drive, period… if there is any drive in your Mac Pro that is bad, dying, dead, not working that well, especially one that will not mount/show up.. then that’ll stop startup or installation… you could restart, holding down the “D” key on your keyboard ( which must be usb+ wired) and you’ll get to Apple Diagnostics which will basically test all necessary basic components of your Mac Pro… giving them either a Pass or Fail… if something fails, then it must be replaced, eg in the case of a hard drive/ssd if there are problems that disk utility cannot and won’t fix, then that hard drive is dying/on its way out/ about to be toast, is unreliable.. I hope that you did and have a backup of your main hard drive( s) via Time Machine… otherwise you might be able to network to another Mac- and via Target mode, backup/recovery/save your data/stuff.. otherwise you’d have to buy and use a data recovery/rescue utility/application and hope/pray/cross your fingers that it works well enough to get your drive functioning , such that you can either try method 1 or method 2.. burning a whole bunch of DVD’s or using a big enough usb stick or properly formatted usb external drive to recover/save/get all your stuff/data.., if not there are conpanies that specialize in data recovery , but they are expensive, very expensive

John B

The definition of a dead drive:

A drive that will not tell disk Utility its name and a reasonable non-zero size/capacity cannot be repaired, erased, or used.

if it has appropriate cabling and power, it has died.