Resolving “STOP 0x0000007B INACCESSIBLE_BOOT_DEVICE” after you make changes to your hard drive configuration

I’d heard that, unlike previous versions of Windows, a Vista installation could be moved to a new computer without any problems, and would just re-detect all the hardware and reconfigure itself. So when I got my new computer, I imaged my boot partition to the new hard drive (it was much bigger than my old one), attempted to boot Vista, and got this error:

STOP: 0x0000007B (0x818B51B0, 0xC00000010, 0x00000000,0x00000000) INACCESSIBLE_BOOT_DEVICE

WTF? After much digging, it turns out that my new motherboard had AHCI enabled by default, whereas my old one didn’t. This is a SATA standard that supports Native Command Queuing (NCQ), special power management, and some other features. While Vista supports it out of the box, if no AHCI drives are connected when Vista is installed, it disables the drivers, and any attempt to switch to AHCI mode later will give you a blue screen at boot time. The general consensus online is that you have to reinstall Windows, but you do not!

To resolve the error:

1. In the system BIOS, switch AHCI mode off. This will probably mean something like “Compatibility mode” for the drive – look for a setting that sounds like it does this, either for the controller or the drive itself. This will allow you to boot into Windows again
   1. a.  If you still can’t boot into Windows, you may need to rebuild the boot sector – not as scary as it sounds! Boot the the Vista install DVD, and when prompted, select “Repair installation”. After thinking for about 15 seconds, the install should say that it’s found the problem and corrected it, and you can reboot – Vista should come right up after that.
2. Once you’re in Windows, load REGEDIT and navigate to [HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Msahci]
3. Set the value “Start” to “0”. This will tell Windows to search for AHCI drives when it boots.

Reboot, and switch your hard drive back into AHCI mode when you do. Windows will boot, detect it, and install drivers. It will probably ask you to reboot again

1. Resolved! Windows boots on your old Vista installation. Aside from this minor hiccup, Vista did indeed cooperate with my new hardware – it detected everything and came right up. It asked me to reactivate, but since it’s a corporate copy, that was no big deal.