yes the ssd boots with the hdd plugged up and everything but nothing will appear anywhere but if I take ssd out the hdd boots up just fine and both have windows 10 64bit
Was the hdd an upgrade from win 7/8 or a fresh install of win 10?
So both will boot with other removed? Means when you installed win 10 on ssd it never added its boot details to hdd boot partition - this is a good thing, in a way.
It could be because they are both win 10. Both would be fighting for control and I expect SSD only wins as its 1st in boot order? Not sure why it cannot see other install.
I would copy everything off old hdd, and then wipe it using diskpart (see below), and then put ssd back in and though hdd won't show in boot order, it should appear for drive management and let you format it again as a storage drive
boot from installer
on screen after languages, choose repair this pc, not install.
choose troubleshoot
choose advanced
choose command prompt
type
diskpart and press enter
type
list disk and press enter
this shows all drives available, DVD/USB and hdd, make note of hdd number
type
Select disk X - where X is the number of the hdd you want to wipe, change X to that number and press enter
once the drive you want to install on is chosen, type
Clean