1) Make sure the HD Drive is showing in BIOS.
2) Check all the cables.
3) Check the hard drive with the manufacturer's diagnostic tools. Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp. HD Diagnostic
I am pretty sure the drive is showing up but I will check for that when I get home tonight. I want to add that I had been receiving the error message about no boot sector for about 3 months and if I hit the F1 key it would boot up with no problems and work all day. I go a new laptop so I thought I'd fix the old one for my kid. I figured it would be easier to fix the computer than reminding him to hit the F1 key when the error message pops up.
Looking at your avatar makes me want to say ouch! Is that your leg or arm? Must make the metal detectors go nuts at the airport.