Hi, I've been experiencing the following symptoms intermittently over the past several months. I am out of apple care since early 2009 and could use some help narrowing down the root of the problem. I've already ran the Apple Hardware Diagnostics Extended Test with no problems reported. Mac Pro 1,1 early 2006, 2x3.0Ghz(Woodcrest dual-core), 8gb ram, 8800gt, 2x750gb seagate and 2x320gseagate running 10.6.2 1. (Energy Saver configured to NOT turn off hard drives when not in use) Sometimes the computer will hang with the spinning mouse cursor while the hard drive appears to power off and back on. I have 4 drives in the computer in 2 raid(1) arrays, one OS, one Time Machine. Both arrays are healthy and have passed Drive Fitness tests. If I pull 2 of the 4 drives out, the symptom goes away. EDIT: if problem persists, kernel panic comes shortly after. if the hard drive spins back up, everything goes back to normal until the next time the hard drives power off again. These are drives that past Seagate's own diagnostics utilities. 2. From a cold start, the computer sometimes will not start pushing the power button. Nothing spins up, but you get a single click as if it's working, but no fan and no hdd spool up and no video. If I wait a while and try again, it will work. Probable causes: power supply and/or motherboard. Question is, how do I determine which before I buy a replacement part for the swap? Any ideas?