If you're getting a "STOP 0x0000007B INACCESSABLE_BOOT_DEVICE" error when you're trying to boot Windows, then you'll have to reenable AHCI mode in Windows manually. First, enter your motherboard BIOS (press the Delete key to open the BIOS on Gigabyte motherboards) and change your motherboard controller back from AHCI mode to SATA mode (or whatever your motherboard calls it).
Now you can boot Windows again, though Mac OS X will probably be rendered unbootable. Boot into Windows, and run this program. This installer by Microsoft will automatically edit your registry to enable AHCI mode.
If you want to perform this registry edit manually, here are the instructions from the Microsoft help page:
1. Click Start, type regedit in the Start Search box, and then press ENTER.
2. Locate and then click the following registry subkeys:
3. In the right pane, right-click Start in the Name column, and then click Modify.
4. In the Value data box, type 0, and then click OK.
5. On the File menu, click Exit to close Registry Editor.
Now reboot, enter your motherboard BIOS, and switch back to AHCI mode. You should now be able to boot into both Windows and Mac OS X.