I was thinking it could be the BIOS.
Years ago in the mid 90’s I had a black screen and of course we are to make a copy of our hard drive which I never did.
But one can go to Statbles etc they have that CD back up for almost all kinds of computers to restore the BIOS.
How to enter the BIOS or CMOS setup
http://www.computerhope.com/issues/ch000192.htm
How to Set BIOS to Boot from CDROM
http://www.hiren.info/pages/bios-boot-cdrom
Some where among your CD’s that came with the computer you might have that CD!
That is why we moved the drive to an intact machine with a proven BIOS. No Joy. I replaced the BIOS battery in the sick computer as the first effort. Nope, it’s the HD. :-(
LJ's BIOS began to boot and passed the POST (Power on self test), but since the boot device was dead and it could find no other devices to boot from it just threw up its hands in despair, or looped trying to find them.