If it is your problem, here is a work around provided by sminlal in a different thread, which I used when switching my SSD from IDE to AHCI.
OK, so you've just changed the BIOS configuration from IDE to AHCI and it won't boot, is that right? If so, this is how you fix it:
1) Set the BIOS config back to IDE so you can boot Windows and (you guessed it) boot Windows.
2) Run the Registry Editor (regedit.exe)
3) Navigate to Registry Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci
4) Set the "Start" value to 0 (zero)
5) Shut down
6) Start up again, but before Windows boots go into the BIOS configuration screens and change the disk mode to "AHCI". Save the new BIOS configuration and restart so that Windows boots.
When Windows starts, it will detect the change, load new disk drivers, and do one more reboot to start up with them.