I have a hp pavilion dv9823cl ... recently the laptop suddenly showed me the error message Operating System not found.. And i noticed in the bios that the harddrive wasnt detected either. I changed the harddrive from the primary slot to the secondary one the laptop had ... and on doing that the harddisk was detected. The problem now is the laptop will not boot from the harddisk as it is in the secondary slot. I wanted to know the possible causes for this and if there is any way to make the laptop boot from the secondary bay (which still has the same harddisk) .. i managed to format the drive and copy the setup files for windows xp onto it using a usb but after the restart the machine will not boot frm the drive since it is in the secondary bay. Also the bios does not have an option as to which harddisk to boot from.