Problem booting from new SSD

28 Dec 2004
Bought a new laptop recently along with an SSD to replace the crappy 1tb drive inside, installed windows 10 from a USB key and it was peachy, decided the laptop was crap and got rid after putting the mechanical drive back in.

I put the SSD in my desktop which already had an SSD boot drive and 2 normal HDD's in RAID 1. Unfortunately the desktop now insists on booting from the new SSD no matter what boot drive I pick from the BIOS. I created a new BCD with both the old and new SSD options but it boots to a black screen if I choose the old drive, if I unplug the new drive though it boots fine. I'm completely stuck! any ideas? TIA