Ok I'm absolutely concerned here. I purchased 2 new 1TB internal drives today for my 2006 Mac Pro, and I had shut it down and let it sit for about an hour before opening it up. I've installed and replaced drives on this machine (and others like it) many times before so I'm well aware of how to do it, but after putting both new drives in sleds 3 and 4 and booting the computer, nothing happens. It gets to the grey Apple and will sit there for about 5 minutes, and then reboot. It will repeat this process continually. I tried removing both of those drives but the same thing happens. Anyone have any idea as to what the heck is causing this?