I recently had to change my on-board drive controller from IDE mode to ACHI mode, due to a new SSD installed. Windows 8.1 was installed with IDE mode by default in BIOS and I had to make the change after this. After attempting to manual change the default set IDE mode to ACHI, in BIOS, I was unable to reboot into my Windows 8.1 install. After doing a small manual change within the Windows Registry, I was then able to change the on-board drive controller from IDE to ACHI and successfully booted to my newly installed Windows 8.1 environment. There seems to be a couple different ways to resolve this issue.
This resource turned out to be very helpful:
IDE to AHCI after installing Windows 8