Mac OS X no longer boots - Vista does though

[Cromulent]

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.

 

[Cromulent]

A little update:

I spent awhile playing around in the terminal from the boot CD to try and get things back on track but even blessing the MacOS volume using the following command had no effect:

bless --folder "/Volumes/MacOS/System/Library/CoreServices" --bootefi --setBoot --verbose

I then had a look through the NVRAM variables and a curious thing showed. Apparantly the boot-args variable was not defined but I couldn't find any documentation on the Apple website about how to actually go about defining one correctly. I am reluctant to go mucking around with boot operations if I am unsure of what they do.

I think the best fix is going to be to rEFIt onto a CD on our iMac, boot from that and try and nuke the current EFI settings and then reinstall it when I get back in Mac OS X.

Opinions still appreciated .