I have a DH67GD motherboard that I am using to boot multiple operating systems from a single 500GB SATA hard disk. The hard disk is partitioned using the GPT partitioning scheme to support booting Mac OS X but, also has a hybrid MBR partition table to support booting Windows 7 in legacy mode as well as an alternative OS called Haiku that is an ofshoot of the BeOS( https://www.haiku-os.org/ ). I want to use the Chameleon boot loader to boot Mac OS since it boots all the installed operating systems without issues. The first four partitions on the disk are a 200 MB EFI system partition (required by Mac OS X), a 100 GB NTFS partition for Windows, a 20 GB partition formatted with the ext3 filesystem for a Linux root partition, and a 20 GB partition formatted with the Be filesystem. If I remember correctly this arrangement used to work fine but, over the years in my efforts to update my Mac OS installation, I updated the BIOS following instructions on a site detailing how to install Mac OS on this particular motherboard. At some point I started getting a message when I attempt to boot that states "A bootable device has not been detected. Please refer to the Product Guide at http://support.intel.com/support/motherboards/desktop/ ".
The curious thing is that during the installation of Windows 7, when the system reboots with the install disk in the optical drive and displays the message "Press any key to boot from CD/DVD", if no key is pressed the computer proceeds to boot from the hard disk without any issues, Also if I press F10 at the splas screen to get the boot menu and select the hard disk, the boot process continues without any further issues, whether the bootloader is the Windows bootloader or Chameleon. It is quite frustrating, having to press F10 everytime the comptuer is started/restarted. Is there a workaround that doesn't require installing a MBR partitioned disk or inserting a USB flash drive with a bootloader. I use the USB stick set up to install Mac OS to boot into Mac OS and reinstall the Chameleon bootloader, but then I have tio leave the USB flash drive plugged in if OI don't want to have to use the BIOS boot menu (F10).
To say that your description of the overall configuration is confusing is certainly an understatement...
Regardless, if you are having to press F10 in order to boot properly, then there is an issue with the configuration of the boot order in the BIOS. In the course of applying BIOS updates, your boot order may have been modified (this happens from time to time). I suggest that you go into BIOS Setup, use F9 to reset its BIOS configuration to defaults and then properly set the boot order per your hardware configuration (as well as any other BIOS configuration changes you absolutely require).
Hope this helps,