Ah, the old "I didn't change anything" immediately followed by "All I did was..." problem.
My suggestion is to go back to the very basics and try to get a working installation of Windows. Remove all PCIe cards except for the video card (if available install the original Mac card). Remove all SSDs and put a spinner back into the first slot. Then attempt to install Windows using a DVD (more reliable than USB as I've had problems with some USB drives failing as installation media).
Since I didn't read every post hopefully this isn't redundant.
EDIT:
I see you've tried some of this. You may want to try the following:
Remove every hard disk except the one you want to install Windows to. This will make the following easier and potentially avoid loss of data from working with the wrong drive.
1. Boot the Windows installation media using the EFI option
2. Choose your keyboard, language, etc. and click "Next"
3. Select "Repair Your Computer"
4. Select "Troubleshoot"
5. Select "Command Prompt"
The following are all typed within the command prompt window (without the quotation marks):
6. Type "diskpart"
7. Type "list disk"
8. Type "select disk n", where n is the disk you wish to install Windows to
9. Type "clean"
10. Type "exit"
Reboot the system and try installing Windows using the EFI option.