Make sure the Windows 7 HD is set as first HD to boot in BIOS setup.
Then check the SATA controller settings as it may have been changed from IDE to AHCI. Try all settings.
If these fail then reset BIOS to defaults to try again: Clear CMOS - 3 Ways to Clear the CMOS - Reset BIOS
If these all fail then work through these steps for Troubleshooting Windows 7 Failure to Boot
which lead up to possible rescue of files if necessary, then running Samsung Recovery or Clean Reinstall - Factory OEM Windows 7
- the latest official installer needed for repairs or reinstall is in Steps 1 and 2.