Everybody on here knows more about this sort of thing than I, but for what its worth, I have been able to explore windows systems using Linux operating systems. Puppy Linux running in RAM, and others running from a live CD. But the environment looks very different, you have to know what you are looking at and know how to use some maybe unfamiliar tools. At least it was like that for me. You can "goof up" easier than you can in windows
DennisD is sort of the resident HD expert on here, and I would defer to his judgement in any situation. but an experiment with Puppy linux would only cost you a CD, especially considering that the XP system you are fixing is not working at all.
... You can't run registry cleaning for a not live OS, ...
Yep, I just skipped that part, cause trying to run a registry cleaner on an OS mounted (running?) on a usb drive which BSODS anyway is too painful to contempate. Maybe Linux will let him see it, maybe he can recognize and fix the issues, maybe ...