Disk Boot Failure, Insert System Disk/NO HD found

I have an HP Media Center 7330n PC running Windows XP that when I try to boot the blue HP screen displays but it goes to DISK BOOT FAILURE, INSERT SYSTEM DISK AND PRESS ENTER.. then after I attempt to boot from a recovery disk.. NO HARD DRIVE FOUND. PC RECOVERY CANNOT BE CONTINUED. PRESS ANY KEY TO CONTINUE.. I have also tried to change the boot order in BIOS to HDD but no help..Does anyone have any insight on how to fix?? thanx