MacBook Pro, 2012, can't get past boot up screen and the progress bar never fills.

Question

Any thoughts on why or a different command that I can try while powering up?
I press the power button, and it dings per usual. Then the first gray screen pops up and it starts spinning. Then a progress bar appears. It fills about a quarter of the way, and then the screen goes black and the computer shuts down.
Any thoughts on why this might be happening and anything I can try to help boot it back up would be great. Thanks!

Answer 1

Then a progress bar appears.
The progress Bar appears when your Boot drive will not mount. It runs a task similar to Disk Utility (Repair disk) and shows you the progress. It is normal for the bar to only fill less than a third of the way.
If your Mac then shuts down, this is because the Repairs could not be completed. Your Boot Drive (either the mechanism or the contents) is in trouble.
Try booting to Recovery Mode, and attempt to make the repairs form there.
If no joy, buy a drive that could replace your Internal drive, and an enclosure to place it in while you Install a new copy of Mac OS X form fundamental sources. Making a complete copy of a drive you know to be damaged is not generally helpful, but may be needed later if you do not have a Backup.
The advice to erase your drive should be ignored. It was invented long ago, when drives cost US$1000, and the prize was getting the drive mechanism working again.