[divergentdave]

You DON'T need to reinstall windows at all, so don't panic, and don't do anything drastic. I have used a Linux LiveCD before, and on that distro too, my windows drive was mounted as read-only to start with. So tell your son that he'll need to re-mount the windows drive as read-write so he can delete the bad file that he found. This can probably be done by right-clicking on the drive from the file manager, but if not, google around for the text-based command you need to do so.

Best of luck.