UNMOUNTABLE_BOOT_VOLUME

A friend of mine have an (very) old notebook running Windows XP, and it came up with this awful message in a Blue Screen:
UNMOUNTABLE_BOOT_VOLUME

The fix was

1. Boot the machine on a installation set (Windows XP CD-ROM)
2. Go to the Recovery Console
3. Run the command "chkdsk c: /r"

The contents of the disk is rescued, but the machine is still due to a replacement...