my mac pro wont boot if 750gb is in it

Put the 750 gb back in and then turn the machine on while holding the option key down (alt), this will hopefully give you a boot select menu. If it brings up a menu but then seems to get stuck without doing anything for ages then put in and hold the C button down after pressing the power button to boot from disk. Once you're up into OS X or the OS X installer, you'll want to get to your system preferences and set your startup disk as your Macintosh HD one (the FreeBSD install could well be set to the startup volume). You may want to use Disk Utility to sort out your 750gb drive to make it more useful anyway. If this doesn't work then I'm afraid I don't know what to suggest!

Hmmm... how old is this 750gb drive? I'd be surprised if it has failed already. Do you have a PC you could put it in? A low level format in the BIOS of a PC could get it working for you. Other than that, you could get an external SATA enclosure or adapter and plug it in when OS X is already live.

Just had another idea, bit off the wall though. Do you have another mac? You could plug in the 750gb into your Mac Pro and boot it holding down the T button to start it in Target Disk mode - then connect it via Firewire to another Mac and use Disk Utility on the other Mac to format the drive.

BTW I think you have to use a wired keyboard for those startup keys.

No, you can leave the other drives in. They'll all pop up under target disk mode.

have you tried your Apple Hardware Test discs?

also does it ever boot at all and what Operating systems are installed on the drives?

I mean is OSX installed on the 750 or is FreeBSD?

if any of the other disks will boot with an OS, it can be pretty assumptive that the culprit is the 750 unfortunately.

however if none of the OS drives are booting, something could be wrong, perhaps bad memory? install any new memory or PCIe cards?


hmmm

ok, hm. i assume tried maybe resetting NVRAM? PRAM?
boot into safe mode or from the OSX Disk Utility and reformat the drive?


like the other person said if you had a PC or ability to low-level boot it, it just might need that kick start.


otherwise if its still under warranty RMA it for a new one.


just seems bizarre it is doing that. especially if it was working before?

If it didn't even activate target disk mode with the drive in then I'm afraid it definitely sounds like its failed. It should still be covered under warranty, I think most hard drives now have a 3 year warranty as standard and, in my experience, hard drive manufacturers are really good at return/replacements - you'll just have to pay for the shipping to them.

Definitely sounds like its faulty then. Sorry.

from my understanding it should have been reset when you did the PRAM reset, excuse my misunderstanding.

then the next step would try a different 750 to see if it replicates.
or try it in an external enclosure.

basically boot up into OSX, place the 750 in an enclosure and plug it in and see if it mounts. if not then most likely osmething failed with the drive.

probably best to get a replacement =\


goodluck!