My main system (Windows 7 UEFI) is on a SSD. I have a 2nd GPT hard drive I use for backup that is not plugged to the computer.
After unplugging the SATA cable of the SSD, I installed Windows 10 UEFI on the 2nd HD so if my SSD fails, I still have a functioning system I can use in the mean time.
The install went fine. But now when I unplug the HD and plug the SSD, Windows 7 won't boot. I think the Windows 10 install messed with the Windows Boot Manager in the BIOS and it prevents me from booting.
I have an image backup of the W7 boot partitions so I think I can restore everything back to normal... except that when I'll do that, Windows 10 won't boot.
So the question is: how can have on the same machine (i7 2600K, Asus P8P67 B2) 2 UEFI Windows (7 + 10) on 2 different drives that are not plugged at the same time?