Right this was caused by me mucking around too much . So I decided to install Ubuntu 9.10 on a separate partition on my Mac Pro but before I did I installed rEFIt 0.13. Things worked well the install completed without incident. Then when I restarted I just got a blank white screen that went no further so I assumed that somehow the startup disk had got a bit mucked up so I restarted again holding "alt" and the only partition that showed up was my Vista partition. So I rebooted yet again with the Mac OS X Snow Leopard DVD and checked out my Mac OS X drive and all the data was still there, I took the oppurtunity to backup what I could and repaired the drive with Disk Utility, still no luck. Then I just decided to format it and reinstall OS X thinking that it would at least get back to usable state but the Mac OS X still won't boot no matter what I do. Does anyone have any suggestions for how I can fix this little mess I have gotten myself into? Thanks.