I have a custom built windows computer that had windows 10 installed on an ssd and games and other stuff on a 1tb hdd. I recently got a 3tb hdd to replace my 1tb. I thought I wouldn't have to clone since this wasn't my os drive, so I simply copied my files from my old 1tb to my 3tb and then disconnected my 1tb. When I booted up again I was told that my "boot configuration data is missing" even though I didn't alter my SSD. After tons of trial and error I decided to disconnect my SSD and just clean install Windows onto my old 1tb, so I could atleast boot it up and then maybe reinstall on my SSD (which hadn't been working). I installed windows 8 fine and then went to upgrade it to 10 only to find that my serial number only worked for upgrades and not clean installs. Great. Well, I reconnected my SSD and turned my computer on and was prompted with a choice between windows 8 or 10. Confused, I chose 10. And I found out that suddenly my old SSD windows was working fine. Thinking the problem was solved, I turned off my computer and removed my old 1tb hdd. But when I turned it on, I got the missing boot configuration error again. I shut down, reconnected my old 1tb hdd that now had windows 8 on it, booted and suddenly my windows 10 SSD install is working again. And now here I am, stuck with an old hard drive I want to replace that apparently has some valuable boot data on it even though windows 10 is on another drive. 2 other things: 1. I checked disk management and it appears that while my SSD is set as boot and active, my old 1tb is set as system and active. 2. I tried changing the boot order in bios and if I force it to boot my SSD or st it first in the boot order, I get the boot configuration missing message again. Sorry if any of this is unclear, im stressed out and typing on my phone. I will post screenshots or more info if needed.