I just installed a 4th hd in my Mac Pro 2.66 Ghz (10.5.1) and when I boot up it just hangs on the grey Apple splash page. The hd just makes a spinning noise and hangs there. If I take the drive out the system boots normally. If I insert the drive while the system is up and try to go to Disk Utility, it hangs trying to detect the drives. I took the drive and inserted into #3 (obviously removing the other #3) and it showed up and was able to format it. But as soon as I put it into #4 SAME PROBLEM. Anybody have any ideas? I've searched all over the internet for the same problem and only found one person with that problem and there was no solution posted. Thanks in advance.