Salut,
tu peux tenter de reparer avec ubcd4win
Go -> Programs -> System Tools -> Check Disk
Type C if this is your partition containing the operating system, adjust according if these files are on a different partition ie D, E etc....
When prompted "Do you want to fix errors ....", enter Y. When prompted "Start check disk?", enter Y.
Then defrag the Hard Drive, you can use Dirms or DefragNT, once complete reboot.
Your system should now boot.
If this still doesn't work you will need to do a repair installation of XP. I haven't received any feedback from these instructions but they should work.
bon courage.