Q: My Mac Pro will only boot about 3/4ths of the way!

Turn on Verbose Mode. Then it will scroll messages up the screen as it boots up. When the messages stop moving, write down the last three lines or so and post them here.

How to start up your Mac in single-user or verbose mode - Apple Support

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there was not text

Then either you did not get into Verbose Mode, or your Mac died before being able to load anything except the boot.efi (which contains the gray Apple logo).

To use "snag keys" at Startup, your keyboard must be connected to a USB port on the chassis, not on a display or other USB Hub.

Can you boot to Recovery?

https://support.apple.com/en-us/HT201314

Are you using a wired KB connected directly connected to one of the mac's USB ports?

Have you unplugged all other peripherals?

Does the screen turn gray? Do you get the dark gray Apple in the center? Do you get any words on the screen? Do you get a progress bar?

Can you boot from an install DVD?

- Try resetting the SMC and NVRAM/PRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

About NVRAM and PRAM

- Try starting in Safe Mode

- What happens when you boot with the Option key depressed?

- Do you hear the startup chime?

I Get a progress bar and the apple but the progress bar only goes about 3/4ths of the way

if the progress bar grows from the left end and fills about 1/3 of the way before stalling, your Hard Drive was found to be too damaged, and could not be mounted. while it is filling the progress bar to this point, your Mac is doing the equivalent of Disk Utility ( Repair Disk [directory]).

-- if this fixes everything in one pass, your Mac will continue to boot up normally.

-- If the drive continues to be unmountable, your Mac may power off, or may crash or behave in unexpected ways.

If you can, boot into Recovery. None of the 42 lb silver tower Mac Pros support Internet Recovery, but the 11 in high dark cylinder does.