I decided to break the RAID1 on my Dell M6500 so I could run Microsoft Server 2012 R2 along with my Windows 7 installation. When the RAID was deleted I thought it would be best to switch my SATA controller over to AHCI since I'm running two Corsair Force GT SSD drives. After changing to AHCI the computer blue screens during boot. I have done it several times before but not often enough to remember what needs to be enabled. This behavior is documented in Microsoft KB922976 (Error message occurs after you change the SATA mode of the boot drive) with automatic registry fix and all. However this is not the complete solution for all situations.
According to the KB you need to enable loading of the AHCI driver, a no brainier! And also enable the Intel AHCI controller driver. But what is not included in the KB article is that the ATAPI driver also needs to be enabled for it to work. If you try to change from ATA to AHCI it is already enabled, if your computer booted with the ATA setting.
So according to the KB you should set these two registry keys to "0":
But you should also check that this one is set to "0":
You can also run these commands instead:
REG ADD HKLM\System\CurrentControlSet\Services\msahci /v Start /d 0 /f /t REG_DWORD REG ADD HKLM\System\CurrentControlSet\Services\IastorV /v Start /d 0 /f /t REG_DWORD REG ADD HKLM\System\CurrentControlSet\Services\atapi /v Start /d 0 /f /t REG_DWORD
Now your computer will start without the blue screen!