SSD Not Detected In Startup

[sloan448]

I have a weird thing going on with my computer. I just took the "current" Ultra M 2 ssd main drive out to put the old one in to get some files off it. When I put the current one back in as the main drive the computer won't detect it in the startup. I put the old one back in and it detects it fine, I am using it right now. I put the current one in an external drive and it shows up and I can access it.

Why would the computer suddenly not see the "current" drive but does the old one?

The current drive is a WD Black SN770 (1tb). The one in the computer is a WD Black SN550? (500gb).

The motherboard is an ASROCK.

[sloan448]

I figured it out. After I disconnected all the other HDs in the computer it booted to the current ssd. One of the drives has an operating system installed on it and I think it got confused. It's an older HD that I haven't taken all the files off I want yet.