|Sounds like a problem with the hard drive - either its died or at least its boot sector has become corrupted. If you go into the bios settings, does the hard drive appear there? If it does, then what I would do is boot into recovery console. At the prompt type chkdsk c: /p|
when complete (if it completes) - should find errors next type
(type Y to any prompts).
Then type exit (to reboot machine). Hopefully now will boot into xp. Otherwise post back with more details please.