Dual booting Mac OS and Windows on the same unit can run into this common problem... especially if the machine was first configured to run windows.
This article from MacBreaker describes the problem and the fix. I have successfully applied this myself and it solved this problem on my build.
Here's an excerpt.
If your Hackintosh is like mine, in which you installed Windows first before installing Mac OS X on a separate hard drive, then you'll notice that you can no longer boot Windows once you've changed the BIOS to AHCI mode (which is necessary for the Mac OS X install). This is because Windows turns off AHCI mode support if you install it while your BIOS is in SATA mode (which is what Gigabyte motherboards call it). Technically, it's recommended that you always switch to AHCI mode before installing any operating system, but how in the world were you and I supposed to know that? Jump past the break[click the link above] to learn how to solve the issue.