Figured out the problem with my computer. Booting it today, found the last two bytes of the MBR were again 55AA, but every odd byte of the MBR had bit 7 set. The block after that didn't. What I surmised was that a temporary hardware failure earlier was masking out that bit on the read, but setting it on the write. So when I had attempted to fix the problem, I made it worse.
Well, I didn't have to fix the whole MBR, only the partition table. My first guess at which bits to clear turned out to be spot-on, and I now have access to all my files again... at least until the hardware problem resurfaces. I just can't boot into Windows again unless and until I complete the repair of the MBR. No great loss. Once I save all the files I need (if any!) maybe I'll overwrite that piece-of-shit operating system and use all that space for something important, like porn.
last updated 2013-01-10 21:18:35. served from tektonic.jcomeau.com