This message is standard, maybe you forgot some cd, pen drive, memory card without the boot sector on the pc and the BIOS software is trying to boot the Operating System where it does not exist. It is a sequence that we can configure, as priority 1 being hard disk, priority 2 cd-rom, ....
Enter the BIOS firmware and configure to boot from the hard drive, you have nothing to lose. I'm not assuming the cable dropped or hard disk faults.
Another option is to redo the boot sector if it is; maybe more than one partition; I do not think it's a disk failure.
You only need find where O.S. it is or reinstall O.S. in last case.
If it does not work, grab the scapulars, talismans and amulets and pray a lot.