Cannot boot from any Mac OS partition but can from an old Win XP Boot Camp partition
Hope I haven't written to much but I needed to include as much detail as possible.
A few days ago I began seeing an odd pixelation on my left monitor at the same time that a picture displaying on the right monitor began to show frizzy color fringing around the person's face, eyes and other distinct features - then a sort of posterization and color shift. I'd seen that twice before and each time everything just froze. I'd hold down the power button to shut down, then reboot - everything was fine for a few days and it started again. This third time I could not boot from Mac OS 10.8.5.
When I tried to boot this time I got a light grey screen, then in a few seconds I'd get the multi-language kernel panic screen. That held for a few seconds and the screen went black - a few seconds after that it seemed to start to boot up - the Apple logo appeared and a few seconds after the gear appeared. The gear would rotate to about where 11:00 o'clock would be and then stop - went to a black screen again, the kernel panic screen, the Apple logo, repeat. I tried the NVRAM reset - nothing happened. I didn't try a SMC reset.
I next tried to boot while holding the option key hoping I'd might be able to boot from my OS 10.11.13 partition or the older 10.6.8. I got the available bootable drives lined up and clicked on 10.11.3 and it immediately went to the Apple Logo and the progress bar began to move left to right - it got exactly midway and stopped. A few seconds later, black screen, kernel panic screen and back to the Apple logo, progress bar - repeat.
That seemed to indicate that it wasn't the 10.8.5 SSD but probably something in hardware or firmware. I opened the machine and removed every PCIe card except for the Nvidia 8800 graphics card, pulled all four drives out and removed 24 GB of RAM leaving the original 2 GB - then moved one of the RAM modules from the top to the bottom RAM tray as required. With everything removed, leaving only the keyboard and mouse I slid in the drive sled with the 10.8.5 drive. Tried to start up but got the same sequence as before. Then I tried to boot from a 10.8.5 USB boot drive and Alsoft's Disk Warrior flash drive. With the Disk Warrior drive I got the Apple logo and gear and the gear just froze - there was now NO black screen or kernel panic screen.
I then remembered when I'd last held the option key at startup I'd seen the recovery partitions for 10.8.5 and 10.11.3 so I reconnected all the drives and tried to see if a recovery partition might do something. It didn't!! Then I noticed the Boot Camp partition with Win XP Pro (a partition on the 10.6.8 drive). I hadn't used that in 4 or 5 years, having Windows running under VM Ware Fusion or lately, Parallels. I clicked on Windows and it just started up! And I could run applications, browsers, etc.
Relief, sort of. So it wasn't RAM or a bad drive or any of the cards I removed or any of the removed peripherals. It appears reasonable that the problem is somewhere in the Open firmware - boot ROM stuff that I know absolutely nothing about.
I've written a lot hoping that someone here might see exactly what I saw and did, and might be able to help with a fix, if possible, or at least let me know what hardware issues I have and if it's fixable (or new logic board, etc.). Any suggestions, gratefully and honestly appreciated.
MartyP
Early 2008 Mac Pro 3.2GHz dual quad CPU's, 26 GB RAM - partitions for Mac OS 10.6.8, 10.8.5 and 10.11.3 and virtually Ubuntu and Windows 8.1 (missed the MS promotion for free Win 10 upgrade).