AHCI problems? Read here!
you most likely came here cause you have a problem with AHCI, either something crashed, your disc wasn't recognized or something similar. Ok, the first problem is that OSX needs AHCI to work. AHCI stands for Advanced Host Controller Interface and is a open interface definition for SATA controllers.
Since this is a very widely used thing, you will have an option in your Bios for this, sometimes it goes by names like SATA Configuration too. If you are unable to find it there and you see an option RAID instead, disable RAID in the Bios first and check if it appears.
Good luck and happy Hackint0shing!