Yesterday, I just bought a new hard disk intended to replace the original damaged hard disk. I inserted the new hard disk and powered up the macpro before holding "C" key to boot to the installation menu. After a couple seconds, the apple icon didn't appear as usual, but flashing a missing folder icon. I wonder what's up to the hard disk.
Well, then it sounds like you may have more serious problems with your MP since it doesn't appear to be able to see the optical drive. It might be time to take it back to Apple.
Pull your old drive already? A system can't boot from even DVD if there is a severely corrupt directory on one of the drives (even booting from DVDs the system scans other drives).