First thing to try is motherboard battery. If it is dead then bios will not autodetect the hard drive though it should say System Disk Not Found. Do you have your hard drive partitioned as C: & D:? Is the back-up on your external drive a clone or a compressed back-up? If it is a clone you may be able to take it out of the case and fit it in the computer and fit your computer hard drive in the external case to see if you can recover data.