PC Doesn't Boot Windows if new HDD is installed

It's set to the SSD I had it originally on, also the "new" hard drive does have Win 10 on it but drivers from the last PC it was on... might that be the conflict?

(It was healthy when I took it out, just didn't use the old system for anything really but storage so I decided I wanted to put it in the current system)
 

Paperdoc

Polypheme
Ambassador
What MIGHT happen is this: when you install the HDD, your BIOS detects that change and, all by itself, re-sets the boot order to use that unit first. You would not know this without checking. So, install the HDD and then boot up immediately into BIOS Setup. Go to where the boot priority is set up and make sure it is still booting from the SSD, AND that the 2TB HDD is NOT anywhere in the boot sequence. SAVE and EXIT and see if that works.