I had the exact same problem. \software or \system got corrupted, and would do so once in a while. Usually the night before a project was due ofr college. Grrrrr.
It was the power supply. Seems the wattage rating was wrong because when I had all my hard drives hooked up the voltage was screwy. Power supply was only a year old too!
Though the Windows or "Bill Gates" virus causes it's own problems, that's for sure.
If you boot from a xp CD and choose repair then it will replace your registry. (or one of those dang options during install) Then you can access without slaving. Or you can boot up using ntfs for dos and access from command prompt. Promash files should fit on a floppy or two I would think.
Or stick the drive in a usb or fw case.