If you just switch a hard drive from IDE to an AHCI disk in the BIOS, you'll notice that you will no longer be able to boot up Windows. (This usually comes into play when switching from a hard drive to an SSD.)
BEFORE you do this, if you make these changes in the Windows registry, you SHOULD be able to switch it to AHCI and then boot up just fine. (as always, backup your stuff and take precautions in case this doesn't work).
- Start up regedit.exe
- Set HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci to 0 (zero)
- Set HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Pciide to 0 (zero)
- Shutdown and change BIOS setting to AHCI before booting