This does sound like a corrupted registry...which could have happened when the machine reset itself with the drive spinning, i.e. the initial cause of the reset may have been hardware related which in turn fragged a couple of sectors on your hard disk and now the reg is corrupt.
Looks like you will have to do a repair job using the XP cd. Hopefully this will work.
If not, if the HD is screwed and you have another one spare, pop the spare in and reinstall XP to the spare HD and copy all your important stuff over. Then reinstall fresh on your original HD (after fully formatting it) and copy your stuff back.
Failing that, try using a Live DVD of Ubuntu or Fedora Core 7 (both Linux). You can google for these. You will need to use a different computer to download and burn these disk images, but basically when done they will boot into a complete OS straight from CD/DVD.
You should then be able to read and write to/from your windows partitions, so you may find you can save all of your important data to an external firewire drive or something.
In any case, when / if you get your stuff back make sure you keep backups of everything that is important to you. I've learned this lesson the hard way so many times now!
Hope this helps.