operating system not found please help

[Desolate]

On my old computer when i go to start it up, i get the message "operating system not found" what could this be? I was told maybe a loose cable? I can get into the bios, and all the boot up set up so i know this pc is not doomed. I got to formating and it shuts down at 30%

 

[IceDigger]

Sounds like the hard drive is dying 100%. Switch it out.