You're going to need some help right now!
You're going to need some help right now!
You're wondering why you can't try different setups—like using 8.1, reducing partition size, or switching to a new drive—and why the experience with XP and 7 didn't work. The issue is that without XP first, you can't install 7, and the MBR needs to be fixed before it will recognize 7.
For the initial version; you've probably understood by now that a new layout for GPT is your best choice. It improves startup times on UEFI, and the only other benefit I'm aware of is its ability to work with bigger HDDs. The approach @cep0_ suggested works well! When using two drives, I currently have setups with both drives and always get the option to boot from one or the other. It's odd that it defaults to just one port. I've only tried two Windows 7s and one with XP/7. To help distinguish them at boot, I change the OS names using a bcdedit command.