Welcome to BC
I've read through your problem and I would be inclined to reformat and install a legitimate
version of XP.
The fact this computer has virtually no updates shows the OS is illegal.
Reformatting with a legal
version will ensure updates are possible and that this won't happen again.
I understand that you would probably want to salvage some documents/files of that computer,
You could boot from a disc and try running the PC in safe mode to copy some files.
The blue screen error with "corrupt
" sounds very grim, and if this XP is illegal there will be no CD,
This rules out the windows repair facility - "sfc
Without knowing what the exact error is it is hard to tell what caused it,
However, without updates/firewall etc it is likely a corruption caused by malware.