Mac Pro startup trouble - White screen with no entry sign

On start up, mac makes startup noise, goes to white screen with Apple Logo and spinny thing at bottom, then after about 2 minutes the Apple Logo changes to a grey No Entry sign. Still the spinny thing at the bottom.

I've tried:

• reset PRAM/NVRAM (same thing)
• holding down "alt" and selecting Windows partition boots to windows perfectly!
• single user mode
• comes up with "Still waiting for Root Device"
• netboot - using deploy studio
• repair disk permissions is Disk Utility
• set startup disk to OS X
• reimage OS X

Found this apple article, although it's dated back to 10.1, and 10.2! Goes on about reseting PRAM, reinstall OS.

Finally, I thought I would try the Hard Drive on another machine, so I "firewired" it up to the machine next to it.

• I booted the broken one off the working one. Worked fine
• I booted the working one off the broken one. Worked fine

So I knew that both installations on both Hard Drives worked fine. To boot I held down "alt" and selected the firewire OSX to boot from. It appeared that using the "alt" key to select an operating system fixed the problem.

I then tried holding down the "alt" button, selected the OS X partition which wasn't working, and it worked fine!!

So, I finally concluded that it was down to the "bless" command you use. The one with Deploy Studio (which is how I set the boot disk originally) seems to not work with this machine.

So, to fix this:

1. I booted the machine on it's normal OS X partition (holding down "alt" to select the OS X partition)
2. Went into "System Preferences" and "Startup Disk"
3. Selected first the Windows Partition, and then the OS X partition

This hopefully set the "bless" command right again.

It worked!!