Lets see if taking my question here helps, Apple Support hasn't... My issue is complex, but I'll try my best to explain it as I can. One has been resolved it seems, but I am including it so that the whole issue can be seen in context. ____________________________________ Friday, May 16, 2014 Last night, after rebooting my Mac Pro from my Bootcamp partition (I'm using Windows 7 Professional if that information is helpful) I received a kernel panic upon Mac OS X booting (Mac OS X 10.6.8). My first action was to launch Disk Utility to verify the Mac HD, verify was stopped by disk utility citing that I should insert my Mac OS X install DVD and repair the disk. I tried booting from my Snow Leopard install DVD. After the grey Apple logo appeared with the gear spinning below it remained for roughly ten to fifteen seconds (a little long) then the Apple logo changed to. A grey prohibitory sign (circle with a diagonal line through it, the spinning gear remained. I tried booting from the Snow Leopard DVD a few time, same result. Following this I tried booting using Disk Warrior, same result again. I tried booting both the Snow Leopard and Disk Warrior DVDs in both my upper and lower optical drives, with no change. I decided to leave the issue and call Apple Support in the morning ____________________________________ Saturday, May 17, 2014 This morning I woke my Mac Pro from sleep, opened Disk Utility and tried verifying the hard drive to see if it was temporary same result, 'please insert the Mac OS X install DVD and repair the drive.' I also tried booting the install DVD again with no result. I then booted my Mac into Safe Mode to check my hardware. Upon opening Disk Utility and verifying my Mac HD the result "Macintosh HD appears to be OK", rand the test again to see if this was an anomaly, but disk returned another pass. I performed a normal restart of my system, although Finder was a little slower to load than normal, the system booted correctly. I then launched Disk Utility and verified the Mac HD, it returned another pass. This confused me, after a call to Apple Support the tech explained that 'sometime a Safe Mode boot will fix problems because it disables all non-essential processes when booting. That makes sense to me. However. The issue of my Mac not recognizing bootable DVDs remains it reads disks correctly, it just will not boot them. ____________________________________ Other steps I have taken to try and resolve this remaining issue. 1. a PRAM reset. No change. 2. an SMC reset. No change. 3. Removal of newly installed RAM. I have tried both running the old and new RAM separately, no change using either combination. 4. Running bootable DVDs in different optical bays. No change from both bays. a. My upper drive is an MCE Blu-Ray/DVD combo drive, but I have booted from this drive before. (Less than six months old.) b. My lower drive is LG DVD-RAM combo drive, I have also booted from this drive before. (Over one year old, replacement for an Apple optical drive.) None of the above steps have helped, I still cannot boot from my optical drives I always receive a prohibitory sign shortly after the Apple logo ____________________________________ Other system information: Mac OS X 10.6.8 8GB of RAM (4 x 2GB) 500GB Western Digital Caviar Blue HDD (less than a year old, boot drive for Mac OS X 10.6.8) 1TB Samsung HDD (for data storage and also containing Bootcamp partition) 2TB HDD (cannot remember manufacturer, contains Time Machine backups, as well as data storage) ATI Radeon HD 5770 with 1GB of VRAM Sorry for the long post but I really need to be able to boot from my optical drives. ---------- I found an old Mountain Lion installation USB flash drive I created a while back. I am able to boot from the ML USB flash drive, but am still unable to boot from my either my Snow Leopard Install DVD or my Disk Warrior DVD. I have verified both DVD and they pass verification tests. This leads me to believe that the problem resides either in the Mac, or in BOTH the Snow Leopard and Disk Warrior DVDs. Since I am able to boot from a USB drive, I will look into the possibility of creating a bootable Snow Leopard drive, and perhaps also a Disk Warrior drive at least until I can resolve the 'not able to boot from DVD' issue.