Recently my Mac Pro would not boot to Mac OS X. When I was restarting the machine I simply got a grey screen, there it stayed until the system loaded my Bootcamp partition. (About 30 seconds) In Bootcamp the drive would not appear, so I started up with the Snow Leopard install DVD, opened Disk Utility to inspect the drive. The drive simply showed up as "media", unformatted, no SMART status available, 0KB disk size. I restarted the machine again in Bootcamp, and voila there was the Mac HD! I was then able to restart in Mac OS X. This has happened about 4 times over the last 24 hours. My guess is the hard drive is about to die, but I'm not sure if it could just be a software issue with Mac OS X. I have the machine backed up with Time Machine, soon worry there, just not sure if I should replace the drive or keep working on it... Any thoughts from anyone? Thanks.