If I understand you correctly this happened while you were installing XP during the format,partitioning phase. If this is correct, then you do not have XP installed on your HDD,and have no O/S to boot to on said HDD. So if you do as mechBgon suggests and set your BIOS to boot to your HDD before your CD then you will still be stuck with the same error. Your BIOS should be set to boot to your CD before your HDD.If it is, then insert your XP install CD and restart your computer after POST checks, watch for the text that will tell you to "Hit any key to boot from CD" when this happens hit a key and let XP start a reinstall, and let XP take care of formatting and preparing your HDD.