The normal reason for this error is that you have left a floppy disk in the drive, nowadays that can also include a USB drive (remove all USB memory devices). If this is not the cause then you may have trouble. Check the BIOS that it set to boot from the hard drive, is the hard drive seen by the BIOS? If not check (refit) hard drive connections) Worst case the hard drive may have failed remove and test on another computer.