Boot into BIOS setup to see if the HD is registering. If so run the HD maker's HD Diagnostic
extended CD scan to check it's condition.
Next boot into System Recovery Options
to run Startup Repair - Run up to 3 Separate Times.
If these fail continue to work through these steps for Troubleshooting Windows 7 Failure to Start
which lead up to if necessary rescuiing your files to run Factory Recovery or the superior Clean Reinstall - Factory OEM Windows 7