Hi, I have a 17inch intel iMac, early 2006 (the first release). A couple of days ago it decided it no longer wanted to boot up. Inserting the install DVD and running disk utilities verify/repair, it said that the volume had an invalid b-tree node size, and attempting to repair the volume failed. Everything is backed up from this computer, so at this point in time I am only worried about getting it running again. So, I dug deeper to resolve the issue. And the plot thickens... I connected this computer to my newer computer in target disk mode via FireWire, and proceeded to run both Tech Tool Pro and Diskwarrior on the drive. Tech Tool Pro indicates that the hardware is fine, a surface scan yielded no bad sectors, and a volume check confirmed the b-tree node errors with the volume. I attempted to rebuild the directory with diskwarrior, but I got the error: 'DiskWarrior successfully built a new directory for the disk named "Macintosh HD". The new directory cannot replace the original directory because the original directory was too severely damaged.' An attempt to rebuild was equally unsuccessful from Tech Tool Pro, and trying the same task from the bootable DVD's yielded the same issues. So, I decided to reformat and reinstall. I did a 7-pass zero Erase of the disk in the hope of the filesystem detecting any bad sectors, but after reformatting the same b-tree node size error and all associated issues in fixing it remain. Of course, I can't install Mac OS X either because it fails validation on install. I also attempted to run apple's hardware test (starting up with D held), but it never gets past the probing stage. At the moment, I have tried everything I can think of. I would dearly love to get this computer running again, so any ideas/help would be greatly appreciated.