My Mac Pro won't boot

Here's how you choose to boot from another drive:

Boot Using OPTION key:

1. Restart the computer.

2. Immediately after the chime press and hold down the

"OPTION" key.

3. Release the key when the boot manager appears.

4. Select the desired disk icon from which you want to boot.

5. Click on the arrow button below the icon.

Downgrade Lion/Mountain Lion to Snow Leopard

1. Boot from your Snow Leopard Installer Disc. After the installer

loads select your language and click on the Continue

button. When the menu bar appears select Disk Utility from the

Utilities menu.

Booting From An OS X Installer Disc

1. Insert OS X Installer Disc into the optical drive.

2. Restart the computer.

3. Immediately after the chime press and hold down the "C" key.

4. Release the key when the spinning gear below the dark gray Apple

logo appears.

5. Wait for installer to finish loading.

2. After DU loads select your hard drive (this is the entry with the

mfgr.'s ID and size) from the left side list. Note the SMART status

of the drive in DU's status area. If it does not say "Verified" then

the drive is failing or has failed and will need replacing. SMART

info will not be reported on external drives. Otherwise, click on

the Partition tab in the DU main window.

3. Under the Volume Scheme heading set the number of partitions

from the drop down menu to one. Set the format type to Mac OS

Extended (Journaled.) Click on the Options button, set the

partition scheme to GUID then click on the OK button. Click on

the Partition button and wait until the process has completed.

4. Quit DU and return to the installer. Install Snow Leopard.

This will erase the whole drive so be sure to backup your files if you don't have a backup already. If you have performed a TM backup using Lion be aware that you cannot restore from that backup in Snow Leopard (see below.) I suggest you make a separate backup using Carbon Copy Cloner.

If you have Snow Leopard Time Machine backups, do a full system restore per #14 in Time Machine - Frequently Asked Questions. If you have subsequent backups from Lion, you can restore newer items selectively, via the "Star Wars" display, per #15 there, but be careful; some Snow Leopard apps may not work with the Lion files.

Do you hear a startup chime? You might try:

Resetting your Mac's PRAM and NVRAM

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

to see if that fixes the black screen issue. When you cannot get even the gray startup screen when booting from an installer DVD that usually indicates some sort of hardware problem. If you have the original installer discs that came with the computer when it was new, then you can run the Apple Hardware Test. I'm afraid this about all I can suggest at this point.

Well, the chime is good news. But too bad nothing else changed. I take it, then, that you are still unable to boot from your retail Snow Leopard DVD? You did not say if you had the original restore discs for the computer.

Do you have another computer with a working optical drive and a Firewire cable you can use to connect the two?

You would be using Target Disk Mode. You connect the Firewire cable between the two computers both of which, in your case, are FW800 ports. You boot the Mac Pro into Target Disk Mode by booting the computer and after the chime pressing and holding down the "T" key until the TDM screen appears.

Then boot the Mini from your Snow Leopard DVD. Now for this to work your Mini must be able to boot from a retail Snow Leopard DVD. That means the Mini must be a Late 2009 or earlier to an Early 2006 model if it has a Core Duo CPU. After 2009 the Minis required a later version of Snow Leopard that was never released on a retail disc.

If you can boot the Snow Leopard DVD, then you can open Disk Utility from the installer's Utilities menu in order to partition and format the third drive and then install Snow Leopard onto that drive.

Now there is a caveat here. TDM will only work with the drive that is in Bay 1 of the MP. So you will need to swap positions and put the Bay 3 drive into Bay 1, and the Bay 1 drive into Bay 3.

OK.

Yes, that's possible. I've used that card in mine for a couple of years now, but there's no rule that says it can't be defective. It's difficult, however, to work on hardware through these forums. You are wise to take it in for repair under the circumstances.

My macpro won't start (actually stops 1 second after pushing the power button) at home but works perfectly well at the repairer. Could someone help me with that problem please?

I tried to connect an external DVD drive and put in the snow lepoard discs and held C but still nothing.

"C" only boots from a DVD in the Internal drive.

To boot from an External drive, hold Alt/Option (one key) and wait for it to show you what is available. Then choose the best and proceed.