Correction: XP doesn't have SATA or SCSI drivers. And in the case of a downgrade this is a known problem. The first option would be to try to get safe mode or another repair option on the F8 menu. otherwise use the BBS popup or whatever you call it thats usually at F12 during BIOS to boot from your XP install CD. note: If your cd is an upgrade it may not work. and if it asks you to format during setup which is likely and want to get your data ask a freind for a linux live cd and back it up to and external hard drive.