I suggest you enable it in the BIOS first and do a fresh install of Windows 8 to avoid the problems I got.
This isn't easy I recently did it after I updated my BIOS, and I also have a tri-boot configuration if you enable it in the bios you will have to do a full reset because I kept getting endless reboot errors with my Windows 8 installation.
I made registry modifications in Vista and Windows 7 by following these steps:
1. Startup "Regedit
2. Open HKEY_LOCAL_MACHINE / SYSTEM / CurrentControlset / Services
3. Open msahci
4. In the right field left click on "start" and go to Modify
5. In the value Data field enter "0" and click "ok"
6. exit "Regedit"
7. Reboot Rig and enter BIOS (hold "Delete" key while Booting and enable ahci in the BIOS) or whatever key is specified on your motherboard manual or if this is a store bought system your user guide.
If you have Windows 8 installed you have to make a slightly different modification in the registry for me that didn't work so I did a reset and Windows 8 was bootable.
It is slightly different in Windows 8:
Exit all applications
Go to the start screen and type in regedit.
If you see the UAC (User Account Control) dialogue box, just click continue.