it's normally an indication that either
you're trying to boot off a floppy
your hard disk isn't formatted/partitioned/installed
Your hard disk hasn't been recognised by the bios
You've got the wrong drive set as the boot drive (can happen if you add a new disk and don't check).
steps to take
1: check there is no floppy in the drive - if fitted
2: Check the bios is seeing the hard drive, and that your boot order is correct (if you've got 2 drives, make sure the right one is set as boot)
a
And work from there.