If you've run Disk Utility on your Mac hard drive (mine is a Macbook Pro running OS X 10.5 Leopard) and it reports that it cannot fix the disk because of a Invalid Node Structure, your disk may be in trouble. Sometimes this happens because your Mac lost power while it was running. Other times, it may be a sign that your disk may be starting to fail. Anyway, the first order of business is to backup your files. After we backup, we'll fix the problem.

Backing Up

Hopefully, you've got a recent backup. If not, what I did was to bring my Macbook next to a working Mac (this is where Mac-owning friends and family come in handy). Start up your Mac in Firewire Target Mode by holding the T key while booting up. You should see a Firewire logo on your Mac's screen pretty quickly.

Now connect your Mac to your friends' Mac with a Firewire cable. After several minutes, your hard drive will now show up on your friends' Mac as a disk drive. It may take a long while before it appears. When it does appear, it may warn you that your disk has been mounted in a limited fashion.

Browse your disk and copy as much information as you can from your home directory to your friends' Mac. Double-check the files after you've copied them to make sure your files are safe and intact.

Fixing the Invalid Node Structure problem

Next, I purchased ALSOFT DiskWarrior. DiskWarrior is the #1 hard drive fix-it tool for dire situations. Usually, I tell people the Disk Utility will solve 99% of their problems, so DiskWarrior isn't necessary. But if you have the Invalid Node Structure problem, Disk Utility and the fsck_hfs terminal command won't do the trick. DiskWarrior was the only thing that worked for me.

Anyway, download and install DiskWarrior on your friends' Mac. When you run DiskWarrior, it should see the Firewire drive (your Mac) and give you the option to Rebuild it. Go ahead and Rebuild, and follow the prompts.

When the Rebuild is complete and you have accepted and written the changes, unmount your Mac from your friends' Mac. The power you Mac off and restart. It booted up just fine for me - I hope it is works for you as well!