Check these keys for Intel chipset, set to 0

>HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Msahci

>HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IastorV

Changing from RAID to AHCI, you may need one more step. Msahci driver requires Atapi.sys miniport to be loaded during boot as well.

>HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\atapi


For AMD chipsets

>HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\nvstor

>HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\nvraid

>HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\amdsata (non raid)